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Ferreira, Paulo José Gonçalves. "Nanotubos de carbono: simulação computacional, DFT e DFTB." Universidade Federal de Juiz de Fora (UFJF), 2013. https://repositorio.ufjf.br/jspui/handle/ufjf/5456.
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Neste trabalho e apresentado um conjunto de resultados obtidos via simulação computacional para o módulo de Young de nanotubos de carbono do tipo armchair. Os casos tratados são os CNTs de coordenadas quirais (6; 6) perfeitos; com defeitos estruturais de vacâncias; com defeitos do tipo Stone-Wales; e por fim o caso no qual o tubo (6; 6) perfeito e interno a outro de coordenadas (11; 11), também perfeito, em con figura ção de parede dupla. O objetivo final e fornecer uma comparação, em relacão a precisão e ao custo computacional, entre a utilização de dois diferentes pacotes capazes de simular o comportamento dos nanotubos: o programa SIESTA, baseado na Teoria do Funcional da Densidade (DFT), e o programa DFTB+, baserado na aproximação Tight-Binding com DFT. Ao longo do trabalho são trazidas também algumas explicações sobre o interesse nos nanotubos de carbono, a m de validar seu estudo, e a caracterização dos diferentes tipos conhecidos. E também efetuada uma descrição geral das simulações computacionais e das teorias nas quais se baseiam os programas utilizados.
This work presents a set of results, obtained by computer simulation, for the Young modulus of (6; 6) armchair type carbon nanotubes. Cases covered are the (6; 6) perfect nanotube; with vacancy structural defects; with Stone-Wales defects; and nally a multiwall case with (6; 6) and (11; 11) perfect tubes. The ultimate goal is to provide a comparison, regarding accuracy and computational cost, between the use of two di erent packages capable of simulating the behavior of these nanotubes: the SIESTA code, based on Density Functional Theory (DFT), and the DFTB+ code, based on Density Functional Tight-Binding scheme (DFTB). Throughout the work are brought some explanations about the interest in carbon nanotubes, in order to validate the study, and the characterization of di erent types known. It is also given an overview of computer simulations and theories in which are based the programs used.
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Jardillier, Nicolas. "Etude DFT de sites cationiques de la zéolithe CuIY : développement et méthodologie : OCECP et DFTB." Montpellier 2, 2006. http://www.theses.fr/2006MON20091.
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Les zéolithes Y de type Faujasite ayant un rapport Si/Al supérieur à 1 ne sont pas rigoureusement périodiques bien que globalement organisées. De ce fait et de par la grande taille de ces systèmes, pour étudier localement les sites actifs de cette zéolithe une approche cluster est utilisée. Les résultats de modélisation par des calculs quantiques (Density Functional Theory, DFT) des sites cationiques des zéolithes CuIY et NaY, montrent que seuls les sites I, I’ et II sont occupés. Dans cette approche, la taille du modèle ainsi que les atomes saturant les liaisons pendantes sont des facteurs primordiaux. Une amélioration possible de la description des bords des clusters est l’utilisation de pseudo-atomes, « OCECP » (Capping Electron Core Potential), obtenus par un algorithme génétique. Les clusters saturés par les OCECP ont l’avantage d’introduire des charges plus proches du solide réel. Une deuxième méthode, SCC-DFTB (méthode semi-empirique), basée sur une stratégie de pré-optimisation de grands systèmes permet une économie de temps de calcul et apporte un outil supplémentaire pour l’étude des matériaux. Le développement de ces deux méthodes, utiles pour des études par une approche cluster de systèmes de grandes tailles dans le domaine des zéolithes (ou d’autres matériaux nanostructurés), s’inscrit dans l’évolution que suit la modélisation pour être utile à l’expérience, notamment en constituant une perspective vers des calculs du type DFT/DFTBY Faujasite type zeolites with a Si/Al ratio higher than 1 are not rigorously periodic although they are globally organized. As a consequence and from the fact that these systems are very large, a cluster approach was used to model the local active sites of the zeolite. The results of modelling by quantum calculations (Density Functional Theory, DFT) of the cation sites of zeolites CuIY and NaY, show that only sites I, I' and II are occupied. In this approach, the sizes of the model as well as the atoms saturating the dangling bonds are paramount factors. A possible improvement of the description of the edges of the clusters is the use of pseudo-atoms, “OCECP” (Capping Electron Core Potential), obtained by a genetic algorithm. The clusters saturated by the OCECP have the advantage of introducing charges closer to the real solid. A second method, SCC-DFTB (semi-empirical method), based on a strategy of pre-optimization of big systems allows a saving in computing time and brings an additional tool for the study of materials. The development of these two methods, useful for studies by a cluster approach of big size systems in the field of zeolites (or other nanostructured materials), falls under the evolution that modelling follows to be useful for the experiment, in particular by constituting a perspective towards DFT/DFTB calculations types
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Zobelli, Alberto. "Electron beam generation and structure of defects in carbon and boron nitride nanotubes." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2007. http://nbn-resolving.de/urn:nbn:de:swb:14-1197988167199-13274.
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The nature and role of defects is of primary importance to understand the physical properties of C and BN single walled nanotubes. Transmission electron microscopy (TEM) is a well known powerful tool to study the structure of defects in materials. However, in the case of SWNTs, the electron irradiation of the TEM may knock out atoms. This effect may alter the native structure of the tube, and has also been proposed as a potential tool for nanoengineering of nanotubular structures. Here we develop a theoretical description of the irradiation mechanism. First, the anisotropy of the emission energy threshold is obtained via density functional based calculations. Then, we numerically derive the total Mott cross section for different emission sites of carbon and boron nitride nanotubes with different chiralities. Using a dedicated STEM microscope with experimental conditions optimised on the basis of derived cross-sections, we are able to control the generation of defects in nanotubular systems. Either point or line defects can be obtained with a spatial resolution of a few nanometers. The structure, energetics and electronics of point and line defects in BN systems have been investigated. Stability of mono- and di- vacancy defects in hexagonal boron nitride layers is investigated, and their activation energies and reaction paths for diffusion have been derived using the nudged elastic band method (NEB) combined with density functional based techniques. We demonstrate that the appearance of extended linear defects under electron irradiation is more favorable than a random distribution of point defects and this is due to the existence of preferential sites for atom emission in the presence of pre-existing defects, rather than thermal vacancy nucleation and migration.
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Meziane, Mehdi. "Étude de la dynamique électronique ultra-rapide suivant l’ionisation de la molécule de Caféine par la méthode TD-DFTB." Thesis, Lyon, 2019. http://www.theses.fr/2019LYSE1113/document.
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Depuis la fin des années 80 et l'avènement de la femto-chimie nous pouvons sonder la dynamique nucléaire à l’œuvre au cours de réactions chimiques à l'échelle de la femtoseconde. Plus récemment, la production d'impulsions lasers attosecondes isolées permet d'atteindre une résolution temporelle plus grande encore. Par elle, il devient possible de sonder la dynamique d'origine purement électronique induite par photo-excitation, et notamment photo-ionisation. Dans ce contexte, avec le développement des techniques de spectroscopie résolue en temps, il est important de disposer d'approches théoriques fiables aidant à l'appréhension de résultats toujours plus nombreux dans ce domaine. La tâche et néanmoins rendue difficile par le caractère profondément multi-électronique des processus en jeu. Traiter de tels effets précisément requiert une grande puissance de calcul, ce qui a limité les études disponibles aujourd'hui à de petits systèmes. Au cours de cette thèse, j'ai tenté d'expliquer les résultats d'une expérience de type "pompe-sonde" (UVX-IR) sur molécule de Caféine menée par une équipe de collaborateurs à l'Institut lumière matière. J'ai utilisé pour cela une méthode basée sur la théorie de la fonctionnelle de la densité dépendante du temps, la TD-DFTB dont le coût numérique réduit par rapport à cette dernière permet des calculs sur de gros systèmes en temps raisonnable. J'y présente une étude du paysage énergétique de la Caféine ainsi que le résultat de 2 approches distinctes pour simuler l'ionisation de ce composé. La première, l'approximation de l'ionisation soudaine cosiste à retirer "à la main" un électron à l'une des orbitales Kohn-Sham occupées du système neutre et ne tient pas compte du champ laser. La seconde à recours à un potentiel imaginaire (ou CAP - Complex Absorbing Potential) pour simuler la perte d'electrons, et tiens explicitement compte du champ laserSince the advent of femtochemistry, at the end of 1980's, we are able to probe the nuclear dynamics underlying chemical reactions down to the scale of a femtosecond. More recently, the production of isolated attosecond pulses allows to reach an even bigger temporal resolution. It is now possible to probe the ultrafast electronic dynamics following a photo-excitation. In this context, with the developpement of time-resolved spectroscopy techniques, it is important to have reliable theorectical approaches in order to apprehend the increasing number of results in this field. This task is made difficult by the intrinsic multi-electronic nature processes at play. The precise treatment of such effects requires a considerable computing power, and have thus limited the availables studies to relatively small systems. In this thesis, I tried to explain the outcome of a "pump-probe" (XUV-IR) experiment on Caffeine molecule realized by our collaborators at the Insitut Lumière Matière. To do so, I used a method based on density functional theory, the TD-DFTB, which lower numerical cost with respect to TD-DFT allows calculation on bigger compounds. I present in the document a study of the energetical landscape of Caffeine, and 2 approaches to simulate ionization. The first one, the so called sudden-ionization approximation consist to retrieve "by hand" an electron from the occupied Kohn-Sham orbitals of the neutral system without taking the laser field into account. The other one is based on the introduction of a complex absorbing potential (CAP) to account for electron loss and take explicitely the laser field into account
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Dontot, Léo. "Propriétés structurales et spectroscopiques des agrégats d'hydrocarbures aromatiques polycycliques." Toulouse 3, 2014. http://thesesups.ups-tlse.fr/4526/.
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La modélisation des agrégats moléculaires neutres ou cationiques représente encore un enjeu difficile pour les approches ab initio dès que les molécules impliquées sont de grande taille ou que leur nombre dépasse plusieurs unités. Nous développons, dans cette thèse, une méthode mixte fondée sur la combinaison de la méthode DFTB, une approximation de la Théorie de la Fonctionnelle de la Densité (DFT), avec un schéma d'Interaction de Configurations (CI). Cette méthode (DFTB-CI) présente une approche originale et efficace permettant une description correcte de la résonance de charge au sein des agrégats cationiques. L'application aux agrégats d'hydrocarbures aromatiques polycycliques intéresse plusieurs domaines tels la physico-chimie du milieu interstellaire, la chimie de l'atmosphère ou encore les processus de combustion. Ce travail a permis de caractériser les propriétés structurales de l'état fondamental des agrégats neutres et cationiques de pyrène et de coronène contenant jusqu'à une dizaine de molécules. Il a nécessité la mise en place d'une stratégie multi-méthodes afin de rendre efficace la recherche des structures les plus stables à l'aide de l'algorithme d'exploration globale, "Parallel Tempering Monte-Carlo". A la suite des propriétés structurales, nous avons déterminé les grandeurs caractérisant la stabilité des agrégats (énergies de cohésion et de dissociation) ainsi que les propriétés électroniques comme la dépendance des potentiels d'ionisation en fonction de la taille, en très bon accord avec les résultats expérimentaux. Finalement, nous avons proposé une extension du modèle DFTB-CI pour calculer les états excités des agrégats moléculaires. Les applications aux dimères sont en bon accord avec les calculs ab initio. Une application aux petits agrégats cationiques de benzène et de pyrène a permis la détermination de leurs spectres électroniques d'absorptionModeling of neutral or cationic molecular clusters remains a challenge in ab initio approaches as soon as the molecules involved are large or when their number exceed several units. We develop, in this thesis, a mixed method based on the combination of the DFTB method, an approximation of the Density Functional Theory (DFT), with a Configuration Interaction (CI). This method (DFTB-CI) provides an original and efficient approach to obtain a correct description of the charge resonance within cationic clusters. The application to polycyclic aromatic hydrocarbons clusters is of interest in various fields such as physics and chemistry of the interstellar medium, chemistry of the atmosphere and also combustion processes. This work has enabled the description of structural properties of the ground state of neutral and cationic clusters of pyrene and coronene containing up to ten molecules. A multi-method strategy has been implemented in order to efficient search for the most stable structures with the global exploration algorithm "Parallel Tempering Monte Carlo". In addition to the structural properties, we have determined the quantities characterizing the stability of these clusters (binding and dissociation energies) as well as their electronic properties such as the dependency of the ionization potentials on the size in good agreement with experimental results. Finally, we propose an extension to the DFTB-CI model in order to compute the excited states of molecular clusters. The results on dimers are found in good agreement with ab initio calculations. An application to small cationic clusters of benzene and pyrene presents the determination of their electronic absorption spectra
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Hazebroucq, Sandrine. "Etude ab initio de la salvatation d'éléments lourds en milieu sels fondus." Paris 6, 2005. http://www.theses.fr/2005PA066143.
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Heine, Thomas. "Die Berechnung von Struktur, Energetik und kernmagnetischen Abschirmungen von Fullerenen und ihren Derivaten." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 1999. http://nbn-resolving.de/urn:nbn:de:swb:14-994313565203-34149.
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Zobelli, Alberto. "Génération par faiseau d'électrons et structure des défauts dans les nanotubes de carbone et de nitrure de bore." Phd thesis, Université Paris Sud - Paris XI, 2007. http://tel.archives-ouvertes.fr/tel-00192710.
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La nature et le rôle de défauts est de première importance pour la compréhension des propriétés physiques des nanotubes monoparoi (SWNT) de carbone et nitrure de bore. Lamicroscopie électronique en transmission (TEM) est un outil très puissant pour l'étude des défauts dans les matériaux mais dans le cas de SWNT les atomes peuvent aussi être éjectés par l'irradiation électronique. Cet effet peut changer la structure initiale du tube mais peut être également vu comme un outil potentiel pour "usiner" des structures nanométriques. Nous avons développé un outil théorique pour la description du mécanisme d'irradiation. Dans un premier temps, nous avons dérivé, par des calculs basés sur la théorie de la fonctionnelle de densité, la carte des seuils d'énergie d'émission. Ensuite, nous avons dérivé numériquement la section efficace total de Mott pour différents sites d'émission dans des nanotubes de carbone et nitrure de bore. Utilisant un microscope STEM, nous avons été capables de contrôler la génération de défauts dans des systèmes nanotubulaires avec des conditions expérimentales optimisées sur la base de nos calculs de section efficace. Défauts ponctuels ou lignes de dislocation peuvent ainsi être obtenus avec une résolution spatiale de quelques nanomètres.
La structure, l'énergie et les propriétés électroniques des défauts ponctuels et des lignes de défauts ont été étudiées dans les systèmes de BN. L'énergie d'activation et les chemins réactionnels pour la diffusion de mono et de bi-lacunes dans du BN hexagonal ont été dérivés en utilisant le "nudged elastic band method" combiné avec les techniques basées sur la fonctionnelle de la densité. Nous avons aussi démontré que l'apparition de défauts étendus est plus favorable qu'une distribution aléatoire de défauts ponctuels et que cela est dû à l'existence de sites préférentiels pour l'émission d'atomes en présence de défauts préexistants plutôt qu'à des phénomènes de migration et nucléation thermique des lacunes.
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Frenzel, Johannes. "Structural, electronic and optical properties of cadmium sulfide nanoparticles." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2007. http://nbn-resolving.de/urn:nbn:de:swb:14-1170678349152-44850.
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In this work, the structural, electronic, and optical properties of CdS nanoparticles with sizes up to 4nm have been calculated using density-functional theory (DFT). Inaccuracies in the description of the unoccupied states of the applied density-functional based tight-binding method (DFTB) are overcome by a new SCF-DFTB method. Density-functional-based calculations employing linear-response theory have been performed on cadmium sulfide nanoparticles considering different stoichiometries, underlying crystal structures (zincblende, wurtzite, rocksalt), particle shapes (spherical, cuboctahedral, tetrahedral), and saturations (unsaturated, partly saturated, completely saturated). For saturated particles, the calculated onset excitations are strong excitonic. The quantum-confinement effect in the lowest excitation is visible as the excitation energy decreases towards the bulk band gap with increasing particle size. Dangling bonds at unsaturated surface atoms introduce trapped surface states which lie below the lowest excitations of the completely saturated particles. The molecular orbitals (MOs), that are participating in the excitonic excitations, show the shape of the angular momenta of a hydrogen atom (s, p). Zincblende- and wurtzite-derived particles show very similar spectra, whereas the spectra of rocksalt-derived particles are rather featureless. Particle shapes that confine the orbital wavefunctions strongly (tetrahedron) give rise to less pronounced spectra with lower oscillator strengths. Finally, a very good agreement of the calculated data to experimentally available spectra and excitation energies is found.
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Frenzel, Johannes. "Structural, electronic and optical properties of cadmium sulfide nanoparticles." Doctoral thesis, Technische Universität Dresden, 2006. https://tud.qucosa.de/id/qucosa%3A23935.
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In this work, the structural, electronic, and optical properties of CdS nanoparticles with sizes up to 4nm have been calculated using density-functional theory (DFT). Inaccuracies in the description of the unoccupied states of the applied density-functional based tight-binding method (DFTB) are overcome by a new SCF-DFTB method. Density-functional-based calculations employing linear-response theory have been performed on cadmium sulfide nanoparticles considering different stoichiometries, underlying crystal structures (zincblende, wurtzite, rocksalt), particle shapes (spherical, cuboctahedral, tetrahedral), and saturations (unsaturated, partly saturated, completely saturated). For saturated particles, the calculated onset excitations are strong excitonic. The quantum-confinement effect in the lowest excitation is visible as the excitation energy decreases towards the bulk band gap with increasing particle size. Dangling bonds at unsaturated surface atoms introduce trapped surface states which lie below the lowest excitations of the completely saturated particles. The molecular orbitals (MOs), that are participating in the excitonic excitations, show the shape of the angular momenta of a hydrogen atom (s, p). Zincblende- and wurtzite-derived particles show very similar spectra, whereas the spectra of rocksalt-derived particles are rather featureless. Particle shapes that confine the orbital wavefunctions strongly (tetrahedron) give rise to less pronounced spectra with lower oscillator strengths. Finally, a very good agreement of the calculated data to experimentally available spectra and excitation energies is found.
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Thunström, Patrik. "Correlated Electronic Structure of Materials : Development and Application of Dynamical Mean Field Theory." Doctoral thesis, Uppsala universitet, Materialteori, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-173300.
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This thesis is dedicated to the development, implementation and application of a combination of Density Functional Theory and Dynamical Mean Field Theory. The resulting program is shown through several examples to be a powerful and flexible tool for calculating the electronic structure of strongly correlated materials. The main part of this work is focused on the development and implementation of three methods for solving the effective impurity model arising in the Dynamical Mean Field Theory: Hubbard-I approximation (HIA), Exact Diagonalization (ED), and Spin-Polarized T-matrix Fluctuation-exchange (SPTF). The Hubbard-I approximation is limited to systems where the hybridization between the 4f-orbitals and the rest of the material can be completely neglected, and can therefore not capture any Kondo physics. It has been used to study the atomic-like multiplet spectrum of the strongly localized 4f-electrons in the Lanthanide compounds YbInCu4, YbB12, Yb2Pd2Sn, YbPd2Sn, SmB6, SmSn3, and SmCo5. The calculated spectral properties are shown to be in excellent agreement with experimental direct and inverse photoemission data, clearly affirming the applicability of the Hubbard-I approximation for this class of systems if we are not focusing on Kondo physics. Full self-consistence in both self-energy and electron density is shown to be of key importance in the extraction of the magnetic properties of the hard permanent magnet SmCo5. The Exact Diagonalization solver is implemented as an extension of the Hubbard-I approximation. It takes into account a significant part of the hybridization between the correlated atom and the host through the use of a few effective bath orbitals. This approach has been applied to the long-standing problem of the electronic structure of NiO, CoO, FeO, and MnO. The resulting spectral densities are favorably compared to photoemission spectroscopy. Apart from predicting the correct spectral properties, the Exact Diagonalization solver also provides full access to the many-body density operator. This feature is used to make an in-depth investigation of the correlations in the electronic structure, and two measures of the quantum entanglement of the many-body ground-states are presented. It is shown that CoO possesses the most intricate entanglement properties, due to a competition between crystal field effects and Coulomb interaction, and such a mechanism likely carries over to several classes of correlated electron systems. The Exact Diagonalization solver has also been applied to the prototypical dilute magnetic semiconductor Mn doped GaAs, a material of great importance in the study of future spintronics applications. The problem of Fe impurities in Cs has been used to study the dependence of the spectral properties on the local environment. Finally, the Spin-polarized T-matrix Fluctuation-exchange solver has been implemented and applied to more delocalized electron systems where the effective impurity problem can be solved as a perturbation with respect to the strength of the local Coulomb interaction. This approach has been used to study the magnetic and spectral properties of the late transition metals, Fe, Co and Ni, and NiS.
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Costa, Marcio. "First-principles Studies of Local Structure Effects in Magnetic Materials." Doctoral thesis, Uppsala universitet, Materialteori, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-179223.
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This thesis focus on the magnetic behavior, from single atoms to bulk materials. The materials considered in this thesis have been studied by computational methods based on ab initio theory, density functional theory (DFT), including treatment of the spin-orbit coupling, non-collinear magnetism, and methods capable of treating discorded systems. Furthermore strongly correlated materials have been investigated using the dynamical mean field theory (DMFT). The uniaxial magnetic anisotropy energy (MAE) of the Fe2P was investigated using the full-potential linear muffin tin orbital (FP-LMTO) method. Based on a band structure analysis, the microscopical origin of the large magnetic anisotropy found for this system is explained. It is also shown that by straining the crystal structure, the MAE can be enhanced further. This opens up for the possibility of obtaining a room temperature permanent magnet based on the Fe2P. The spectral properties of Fe impurities in a Cs host have been investigated, for both surface and bulk systems, by means of combination of density-functional theory in the local density approximation and the dynamical mean-field theory (LDA+DMFT), using two different impurity solvers, the Hubbard I approximation (HIA) and the Exact Diagonalization (ED) method were used. It is shown that noticeable differences can be seen in the unoccupied part of the spectrum for different positions of Fe atoms inside the host. The calculations show good agreement with the experimental photoemission spectra. The stability of the 12-fold metal-phosphorous coordination, existing in the meteorite mineral melliniite has been investigated trough total energy calculations using the coherent potential approximation (CPA) combined with an analysis of the chemical bonds, performed by balanced crystal overlap population (BCOOP). It was shown that its uniquely high metal–phosphorous coordination is due to a balance between covalent Fe–P binding, configurational entropy and a weaker nickel–phosphorus binding. Supported clusters have drawn a lot of attention as possible building blocks for future data storage applications. This topic was investigated using a real space noncollinear formalism where the exchange interactions between Co atoms were shown to be tuned by varying the substrate surface composition. Furthermore the spin dynamics of small Co clusters an a Cu(111) surface have been investigated and a new kind of dynamics, where magnetization switching can be accelerated by decreasing the switching field, has been found. A method for calculating the electronic structure for both ordered and disordered alloys, the augmented space recursion (ASR) method, have been extended to treat non-collinear magnetic order. The method has been used to investigate the energy stability of non-collinear arrangements of MnPt and Mn3Rh alloys.
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Boonchun, Adisak. "First-Principles Calculation of Defect Energies in ZnO and Related Materials." Case Western Reserve University School of Graduate Studies / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=case1310056351.
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Malheiro, Carine. "Adsorption de systèmes gaz/eau en milieu confiné : modélisation par une approche DFT/SAFT couplée à une étude expérimentale." Thesis, Pau, 2014. http://www.theses.fr/2014PAUU3022/document.
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La compréhension des phénomènes d’adsorption de gaz en présence d’eau dans des milieux confinés est une problématique importante tant d’un point de vue fondamental que du point de vue des applications industrielles Les travaux menés dans cette thèse ont principalement porté sur le développement d’un nouveau couplage NLDFT/SAFT-VR (Non-Local Density Functional Theory/ Statistical Associating Fluid Theory for potentials of Variable Range) pour modéliser les propriétés interfaciales et l’adsorption de méthane, d’eau et de leur mélange en milieu confiné. Les résultats théoriques obtenus sur ces fluides ont été comparés avec succès à des calculs de simulation moléculaire. Par ailleurs, des isothermes d’adsorption expérimentales de méthane et d’eau sur des charbons actifs ont été mesurées par la technique gravimétrique sur une balance à suspension magnétique. Afin de pouvoir comparer les isothermes expérimentales et théoriques, il est nécessaire de connaître la distribution en taille de pore des solides poreux. C’est pourquoi un nouveau modèle thermodynamique de caractérisation des milieux microporeux a été développé. Les comparaisons des isothermes d’adsorption de méthane ont montré un excellent accord entre résultats théoriques et expérimentauxUnderstanding the gas/water adsorption phenomena in confined media is an important issue from a fundamental point of view and for industrial applications. The main aim of this thesis was to develop a new NLDFT/SAFT-VR coupling (Non-Local Density Functional Theory/ Statistical Associating Fluid Theory for potentials of Variable Range) to model the interfacial properties and the adsorption of methane, water and their binary mixture in porous media. A successful comparison was found between theoretical results from this model and molecular simulation calculations. Moreover, experimental adsorption isotherms of methane and water were measured on activated carbons by gravimetric method on a magnetic suspension balance. In order to compare experimental and modeled adsorption isotherms, it is necessary to get the pore size distribution of the porous solids. To do this, a new thermodynamic model for the characterization of microporous media was developed. The comparison between adsorption isotherms of methane has shown an excellent agreement between theoretical results and experimental measurements
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Junior, Alberto Torres Riera. "Defeitos em nanofitas de Grafeno zigzag." Universidade de São Paulo, 2008. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-10032009-123202/.
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Grafeno e nanofitas de grafeno vêm, cada vez mais, atraindo o interesse da comunidade científica devido as suas notáveis propriedades. Neste trabalho realizou-se um estudo sistemático da estabilidade de defeitos do tipo divacância, vacância e Stone-Wales em grafeno e nanofitas de grafeno com bordas zigzag. Para tal, fizeram-se cálculos de primeiros princípios, baseados em teoria do funcional da densidade (DFT) na aproximação GGA com o uso de pseudopotenciais ultrasoft e uma base de ondas planas. Também foram feitas simulações de imagens de STM para os defeitos nas nanofitas. Além disso, foram encontrados dois novos defeitos, não publicados em nenhum outro lugar (até onde vai o conhecimento do autor), com energia de formação muito baixa.Graphene and graphene nanoribbons have been attracting a lot of interest from the scientific community because of their novel properties. In this work, a systematic research has been done on the stability and energetics of divacancy, vacancy and Stone-Wales defects in graphene and zigzag graphene nanoribbons. With this goal in mind, ab initio density functional calculations within the GGA approximation, using ultrasoft pseudopotentials and a plane wave basis were done. Also, STM images were simulated for some selected defects. Besides, two new defects, not published elsewhere (to the best knowledge of the author), with very low formation energy are reported.
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Gam, Franck. "Modelization of stable metal clusters containing Group 11 elements." Thesis, Rennes 1, 2018. http://www.theses.fr/2018REN1S048/document.
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Les travaux décrits dans ce mémoire portent sur le calcul de la structure électronique de clusters homo- ou hétéro-nucléaires de métaux du groupe 11, afin d’en interpréter leur stabilité, leur structure et éventuellement leurs propriétés. Nous nous sommes tout d’abord intéressés au fait que, contrairement à leurs homologues de l’or et de l’argent, les superatomes de cuivre sont très rares. Nos calculs montrent que ces derniers sont plus stables que les superatomes d’argent. Néanmoins, les méthodes de synthèse de superatomes par réduction de complexes de Cu(I) par le borohydrure conduisent préférentiellement à la formation de polyhydrures de Cu(I) en raison de leur grande stabilité. Nous nous sommes de plus intéressés à la stabilité de clusters contenant un cœur tétraédrique M16, analogue à celui contenu dans le cluster emblématique [Au₂₀]. Notre étude des clusters organométalliques à 20 électrons. [M₁₆Ni₂₄(CO)₄₀]⁴⁻ (M = groupe 11) indiquent que les quatre entités périphériques Ni₆(CO)₁₀ font partie intégrante du superatome, suggérant que [M₁₆]⁴⁻ n’est pas viable. Des calculs sur plusieurs séries de systèmes homo- ou hétéro-nucléaires nus proposent de contourner cet écueil soit en réduisant le nombre d’électrons à 18, soit en incorporant un élément encapsulé au centre de l’entité tétraédrique. Dans une autre étude, nous avons exploré la possibilité de dopage du cluster icosaèdrique à 18 électrons [WAu₁₂] par des atomes de platine (donneurs de 0 électron), soit [WAu₁₂Pdₓ] (x = 1-4). Le calcul indique que certains isomères sont viables et présentent un large spectre d’absorption UV-vis leur conférant des applications potentielles. Enfin, nous avons étudié la structure électronique de clusters organométalliques apparemment très déficitaires en électrons, [Cu₃Zn₄Cp*5] et [Cu₂Zn₅Cp*₅]⁺ et montré que ce déficit n’est aussi important qu’il n’apparaîtThe work described in this manuscript concerns electronic structure calculations of homo- and hetero-nuclear clusters made of group 11 metals, in order to rationalize their stability, structure and in some cases properties. We have first looked at the fact that copper superatoms are very scarce, contrarily to their gold and silver counterparts. Our calculations indicate that copper superatoms are more stable than silver superatoms. However, the synthetic process based on the reduction of Cu(I) complexes by borohydride leads preferentially to the formation of very stable Cu(I) polyhydrides. On the other hand, we have looked at the stability of clusters containing a tetrahedral M₁₆ core similar to the one contained in the emblematic [Au₂₀] cluster. Our investigation of the 20-electron organometallic clusters [M₁₆Ni₂₄(CO)₄₀]⁴⁻ (M = group 11) showed that the four peripheral Ni₆(CO)₁₀ units are full part of the superatom entity, suggesting that the [M₁₆]⁴⁻ entity is not viable. Calculations on several homo- and hetero-nuclear series of bare species indicate that this instability can be avoided either in reducing the electron count to 18, or in incorporating a supplementary element in cluster center. In another investigation, we explored the possibility of doping the icosahedral 18-electron [WAu₁₂] cluster by 0-electron donor platinum atoms, namely [WAu₁₂Pdₓ] (x = 1-4). Calculations indicate that some isomers are stable and have a large spectrum of UV-vis absorption, providing them potential applications. Finally, we have investigated the electronic structure of organometallic clusters, [Cu₃Zn₄Cp*5] and [Cu₂Zn₅Cp*₅]⁺, which are apparently extremely electron-deficient and showed that this deficiency is not as large as it appears
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Potluri, Uma Sadhvi. "Field-Programmable Custom Computing Machines for DFT/FFT and DCT/DST Algorithms." University of Akron / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=akron1383599754.
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Franczak, Agnieszka. "Étude expérimentale et théorique du mécanisme d’électrodéposition de films à base de cobalt : modélisation et relation structures-propriétés par l'approche multi-échelle." Thesis, Reims, 2013. http://www.theses.fr/2013REIMS014/document.
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Des études expérimentales et théoriques du mécanisme d'électrodéposition de différents revêtements à base de cobalt : le cobalt métallique, les alliages binaires Co-Ni, Co-Cu et l'alliage ternaire Co-Ni-Cu sont menés.Les propriétés de ces films dépendent fortement des paramètres expérimentaux tels que le pH de l'électrolyte, la nature du substrat, etc.. Un champ magnétique jusqu'à 12T est superposé parallèlement à la surface de l'électrode de travail. La convection forcée induite dans l'électrolyte modifie les conditions hydrodynamiques et par conséquent, influe sur la structure et la morphologie des films obtenus. Par ailleurs, la cinétique des processus et la croissance des cristaux sont améliorées dans des conditions magnéto électrochimique. Les microstructures obtenues suite au procédé électrochimique en présence d'un champ magnétique sont caractérisées par différentes propriétés magnétiques trouvant un intérêt potentiel en tant que matériaux magnétiques doux et / ou dur. Dans le cadre du projet ANR COMAGNET, les matériaux subissent ensuite un traitement thermique en présence d'un champ magnétique, des phénomènes de recristallisation et interdiffusion sont mis en évidence induisant des modifications des propriétés magnétiques.Enfin, des calculs de l'énergie d'adsorption de l'atome d'hydrogène et de l'ion H+ sur différentes faces cristallographiques du cobalt sont menés par modélisation DFT (Théorie de la Fonctionnelle de la Densité). Ces résultats, mis en relation avec l'étude expérimentale, montrent le lien entre la formation de certaines structures cristallographiques et l'évolution simultanée de l'hydrogène à la surface de l'électrode pendant l'électrolyseThe present work is focused on the experimental and theoretical studies of the electrodeposition mechanism of Co-based films, including single Co, binary Co-Ni, Co-Cu and ternary Co-Ni-Cu alloy films. The modeling and structure-properties relationship by a multi-scale approach is investigated.The preliminary study involves determination and optimization of the electrodeposition parameters in order to obtain nanocrystalline films with satisfied surface quality and promising magnetic properties. It is shown that the electrolytic pH, to-be-deposited type of substrate and deposition time are of high importance in the fabrication of nanoscale materials. Among them, the electrolytic pH is the one, which has the greatest effect on the structure formation. The film growth as well as its quality can be strongly affected by a superimposition of an external magnetic field. The electrodeposition process was carried out under parallel to the electrode surface magnetic fields with magnets strength up to 12T. The results reveal that the induced forced convection in the electrolyte changes the hydrodynamic conditions and thus, affects the structure and morphology of the obtained films. Furthermore, the process kinetics and crystal growth are enhanced under magnetic electrodeposition conditions.Microstructure formed by the electrochemical processing is characterized by some significant magnetic properties, which may result in soft and/or hard magnetic materials, depending on their application approach. Additionally, the microstructure of films has been improved by the magnetic annealing treatment. Thus, the recrystallization and interdiffusion phenomena are observed, and modification of the magnetic properties is induced.Considering the electrodeposition process carried out in aqueous solutions the secondary process, which is the hydrogen evolution reaction (HER), needs to be taken into account. The theoretical study based on the tools of quantum mechanics (QM) and density functional theory (DFT) is used to determine the adsorption energies of hydrogen. In this work, the calculation results are related with the experimental study and may explain the structure formation assisted by the simultaneous evolution of hydrogen at the electrode surface
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Che, Xiaoyang. "Étude théorique de matériaux pérovskites halogénées." Thesis, Rennes 1, 2018. http://www.theses.fr/2018REN1S040/document.
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Cette thèse est entièrement consacrée à l'étude par la théorie de la fonctionnelle de la densité des composés pérovskites halogénés, matériaux prometteurs pour de nombreux domaines applicatifs. Le caractère « hybride » de ce type de matériau est illustré par différentes études de leurs propriétés structurales et électroniques. Le composé tridimensionnel MAPbBr₃ est tout d'abord présenté. Les propriétés électroniques fondamentales telles que les structures de bandes, les états de densité projetée ou les fonctions d'ondes sont discutées. De plus, l'importance du couplage spin-orbite est mise en évidence. L'analyse des symétries est appliquée pour comprendre la symétrie des états électroniques et pour interpréter les propriétés optiques des différents matériaux. Les reconstructions structurales à la surface des cristaux entraînent l'apparition d'effets Rashba-Dresselhaus. Par ailleurs les défauts de surface et leurs passivations sont également étudiés. Des travaux sur les matériaux sans plomb potentiellement moins toxiques sont proposés dans un second temps. Ces études ont pour but d'analyser leurs potentiels pour le photovoltaïque du point de vue des structures électroniques. Différentes stratégies de substitution sont envisagées allant du simple remplacement du plomb à d'autres alternatives plus élaborées comme les pérovskites doubles ou les pérovskites de basse dimensionnalitéThis actual work is entirely devoted to the study of halide perovskite materials, promising materials in many fields of application, by means of the Density Functional Theory. The "hybrid" feature of this type of material is illustrated through various studies of their structural and electronic properties. The three-dimensional compound CH₃NH₃PbBr₃ is firstly presented. Basic electronic properties such as band structures, projected density of states or wave functions are discussed. In addition, the importance of spin-orbit coupling is highlighted. Symmetry analysis is applied to understand and interpret the optical properties of different materials. Structural reconstructions on the surface of the crystals lead the Rashba-Dresselhaus effects. In addition, surface defects and their passivations are also studied. Studies on lead-free materials that are potentially less toxic are proposed in a second step. These studies aim to analyze their potentials for photovoltaic devices from the point of view of electronic structures. Different substitution strategies, ranging from the simple replacement of lead to other more elaborate alternatives such as double perovskites or low-dimensional perovskites are investigated as well
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Azarias, Cloé. "Modeling azacalixphyrin macrocycles." Thesis, Nantes, 2018. http://www.theses.fr/2018NANT4021/document.
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Cette thèse porte sur la modélisation des propriétés structurales, aromatiques et spectroscopiques d'une nouvelle classe de macrocycles alternatifs aux porphyrines, les azacalixphyrines (ACPs). Ces macrocycles conjugués, synthétisés et caractérisés pour la première fois en 2010 par le groupe d’Olivier Siri à Marseille, ont montré des propriétés exceptionnelles (structure, absorption, tautomérie, et complexation). Cette thèse vise à proposer de nouveaux dérivés aux propriétés améliorées, notamment en ce qui concerne leur absorption, en utilisant les outils offerts par la chimie théorique. Parmi toutes les approches ab initio permettant de modéliser les ACPs, la théorie fonctionnelle de la densité (DFT) et sa forme dépendante du temps (TDDFT) ont été principalement appliquées, bien que des calculs utilisant des méthodes alternatives aient également été effectués, notamment à l'aide du formalisme Bethe-Salpeter (BSE/evGW) dans le cadre d'une collaboration avec l'équipe du Dr. Xavier Blase à Grenoble. Trois stratégies chimiques ont été évaluées: (i) l’extension de la délocalisation des électrons en fusionnant plusieurs unités ACP; (ii) la substitution de l’ACP via l'addition de groupes électroactifs; et (iii) le couplage du macrocycle avec un fluorophore présentant une absorption complémentaire afin d'absorber la lumière sur une plus grande gamme du spectre et déclencher des processus de transfert d'énergie entre les sous-unités. Les deux premiers axes ont été réalisés en collaboration avec l'équipe d’Olivier Siri alors que le dernier est le fruit d'une collaboration avec le groupe de Benedetta Mennucci à PiseThis thesis focuses on the modeling of the structural, aromatic, and spectroscopic properties of a new class of macrocycles alternative to porphyrins, i.e., azacalixphyrins (ACPs). These conjugated macrocycles have first been synthesized and characterized in 2010 by Siri’s group in Marseille and revealed exceptional features (structure, NIR absorption, tautomerism, and complexation). This thesis aimed at using ab initio methods to propose new ACP derivatives with improved properties with a focus on their absorption. The Density Functional Theory (DFT) and Time- Dependent DFT (TD-DFT) methods have been predominantly applied, although alternative wavefunction-based theories [the second-order Coupled-Cluster, CC2, and the Algebraic Diagrammatic Construction, ADC(2)] as well as the Bethe-Salpeter formalism, BSE/evGW, have also been used. Three major directions to develop new ACP derivatives have been investigated: (i) the extension of the ACP -conjugation path by fusing several ACP moieties leading to multimers; (ii) chemical modifications of the ACP unit by addition of electroactive groups; and (iii) coupling of the ACP moiety with a fluorophore presenting a complementary absorption spectrum in order to improve the light harvesting and to trigger excitation energy transfer processes. The two former axes have been investigated in collaboration with Siri’s team whereas the latter has arisen from a collaboration with the Mennucci’s group
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Kerber, Torsten. "Dispersionskorrekturen von DFT für Festkörperprobleme." Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2012. http://dx.doi.org/10.18452/16634.
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In der vorliegenden Arbeit wird die Korrektur weitreichender Dispersionswechselwirkungen fuer Dichtefunktionaltheorie fuer Rechnungen unter Anwendung periodischer Randbedingungen erweitert. Am Beispiel des Graphit wird der Einfluss der Dispersionskorrektur auf Strukturparameter und Energien gezeigt. Die berechneten Werte fuer Schichtabstand und Wechselwirkungsenergie stimmen sehr gut mit experimentell bestimmten Daten ueberein. Anhand von Clusterstudien wird gezeigt, dass die Dispersionskorrektur nur sehr langsam mit der Systemgroesse konvergiert. Die genaue Beschreibung der Dispersionswechselwirkungen zwischen Graphitschichten mit der PBE+D-Methode ist nur bei Anwendung periodischer Randbedingungen oder durch eingebettete Clustermodelle moeglich. Der Vergleich der PBE+D- mit der genauen, aber sehr aufwendigen [MP2:PBE + delta-CCSD(T)]-Methode zeigt, dass die strukturellen Unterschiede zwischen beiden Methoden gering sind. Die berechneten Reaktionsenergien unterscheiden sich hingegen deutlich. Die neu entwickelte, effiziente [PBE+D + delta-MP2 + delta-CCSD(T)]-Methode ergaenzt die PBE+D-Energie um zwei Korrekturterme. Der erste Term, die delta-MP2-Korrektur, behebt die Ueberstabilisierung polarer Strukturen (PBE) mit einer MP2-Rechnung am Basissatzlimit. Der zweite Term ueberprueft die delta-MP2-Korrektur durch eine CCSD(T)-Rechnung fuer einen kleinen Cluster. Die [PBE+D + delta-MP2 + delta-CCSD(T)]-Methode wird fuer die Reaktion von C4H8-Kohlenwasserstoffen mit H-Ferrierit angewendet. In der Zeolithpore wurden pi-Komplexe, Butylkationen und Oberflaechenalkoxide als Intermediate identifiziert. Die Isomerisierung von Butenen in der H-Ferrierit-Pore wird mit der Umlagerung linearer Butylkationen in der Gasphase verglichen. Der geschwindigkeitsbestimmende Schritt ist in beiden Faellen die Bildung des tert-Butylkations aus einem methylverbrueckten Butylkation. Die CCSD(T)-Methode ist zur Bestimmung genauer Energieprofile erforderlich.In this work, the long-range dispersion correction for density functional theory is extended to periodic boundary conditions. The influence of the dispersion correction on energy and structural parameters is shown for graphite. The calculated values of the interlayer distance and the interaction energy are in good agreement with experimental ones. By a series of cluster calculations it is shown, that the dispersion correction converges very slowly with respect to the system size. The accurate description of the dispersion interaction between graphite layers requires the usage of PBE+D method applying periodic boundary conditions or embedded cluster models. For structural parameters, the PBE+D methods compares well with the accurate but computationally very demanding [MP2:PBE+CCSD(T)] method. However, the calculated reaction energies differ remarkably. The newly developed, efficient [PBE+D + MP2 + CCSD(T)] method extends the PBE+D energy by two correction terms. The first one, the MP2 correction, rectifies the over stabilization of polar structures (PBE) by a MP2 calculation at the basis set limit. The second term verifies the MP2 correction by a CCSD(T) calculation for a small cluster model. The [PBE+D + MP2 + CCSD(T)] method is applied for the reaction of C4H8 hydro carbons witr the zeolite Ferrierite. Within the pore of a zeolite, pi complexes, butyl cations and surface alkoxides are identified as minima on the potential energy surface. The isomerization of butenes is compared to the rearrangement of linear butyl cations in the gas phase. In both cases, the rate determining step is the formation of the tertial butyl cation from a methyl bridged cation. The CCSD(T) method is for the determination of accurate energy profiles required.
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Farouil, Léa. "Etudes théorique et expérimentale de semi-conducteurs organiques pour l'élaboration d'un biocapteur destiné à la détection de la pollution de l'eau." Thesis, Toulouse 3, 2018. http://www.theses.fr/2018TOU30310/document.
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L'objectif de ce travail de thèse est l'élaboration d'une photodiode organique (OPD) destinée à être intégrée dans un biocapteur. Ce travail s'inscrit dans le cadre plus général de l'étude et de l'amélioration de composants organiques impliqués dans des microsystèmes de détection visant à surveiller la pollution de l'eau. Le besoin d'évaluation et de suivi de la qualité de l'eau suscite un grand intérêt pour des systèmes de détection portables de polluants ayant une réponse rapide et de faible coût. Le principe de la mesure repose sur la détection des variations de fluorescence de micro-algues en présence de substances toxiques. Excitées grâce à une diode électroluminescente (LED) bleue, les algues vont émettre un signal de fluorescence dont l'intensité, modifiée en présence de polluant (Diuron), est détectée par l'OPD optimisée. Le signal de fluorescence à détecter étant très faible, l'OPD idéale doit avoir un faible courant d'obscurité et une grande sensibilité. Cela passe par un choix judicieux des matériaux semi-conducteurs organiques (OSC) entrant dans l'élaboration de la couche active du composant. Pour accompagner le choix des matériaux, il est intéressant d'explorer leurs propriétés physico-chimiques tout en essayant de rationaliser les mécanismes mis en jeu au sein de ces matériaux lorsqu'ils sont utilisés dans l'élaboration d'OPD (phénomènes d'absorption de photons, mécanismes de transport de charges, et pertes associées aux recombinaisons de charges). Cette thèse s'articule autour de deux axes. Le premier axe consiste en une étude théorique qui vise à comprendre et à maitriser l'échange des charges à l'échelle nanométrique par des caractérisations optiques et des calculs de chimie quantique basés sur des méthodes DFT et TD-DFT. L'étude sur un système modèle (le P3HT) a permis d'établir un protocole de calcul très prometteur pour l'étude des propriétés de matériau d'intérêt, en particulier le PTB7. Le second axe est un volet à caractère expérimental. L'élaboration, la caractérisation et l'optimisation d'OPD à base de PTB7 : PC60BM a permis de concevoir un biocapteur algal apte à détecter le Diuron à des concentrations de l'ordre du nanomolaireThe aim of this thesis is to develop an organic photodiode (OPD) designed to be integrated into a biosensor. It is part of the broader framework of studying and improving organic components involved into devices devoted to water pollution monitoring. The need for such portable, fast-response, low-cost microsystems is of great interest. The measurement is based on the fluorescence detection of micro-algae under toxic substances exposure. The excited algae, under a blue light emitting diode (LED), will emit a fluorescence signal whose intensity, modified because of pollutant exposure (Diuron), is detected by the OPD. Since the fluorescence signal is very weak, the ideal OPD must have a low dark current and a high sensitivity. To achieve this performance, a judicious choice of organic semiconductor materials (OSC) used for the OPD is required. In addition, it is interesting to investigate their physico-chemical properties by rationalizing the mechanisms involved in the active layer (photon absorption phenomena, charge transport mechanisms, and losses associated with charge recombinations). This thesis is based on two axes. The first one consists in a theoretical study of the charge exchanges at a nanoscale. This have been done by both optical characterizations and quantum chemistry calculations based on DFT and TD-DFT methods. Calculations were performed on a model system (P3HT) thus providing the basis for a very promising computational protocol for studying the properties of materials of interest, for instance PTB7. The second axis concerns the experimental study of the OPD based on PTB7:PC60BM. We have developed, characterized and optimized an OPD guarantying the detection of algal fluorescence without and with Diuron at about nanomolar concentrations
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El, belghiti alaoui Nabil. "Stratégie de testabilité en production des cartes électroniques à forte densité d’intégration et à signaux rapides." Thesis, Toulouse, INSA, 2020. http://www.theses.fr/2020ISAT0018.
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Les étapes de test en production sont basées à ce jour sur des contrôles optiques (AOI), inspection des joints de soudures par Rayons-X (AXI), électriques (ICT) et tests fonctionnels. Face à la multiplication et à la miniaturisation des composants, la cohabitation de plusieurs technologies (numérique, analogique, radiofréquence, puissance…) sur le même PCB (Printed Circuit Board), les moyens de test listés précédemment ne sont plus suffisants pour répondre complètement aux exigences de couverture de tests en production, car peu performants et coûteux en temps de développement et de cycle de test.L'objectif de cette thèse CIFRE avec ACTIA Automotive en collaboration avec le laboratoire LAAS-CNRS est de définir une stratégie de test en production innovante et adaptée aux produits à forte densité en envisageant dans un premier temps toutes les techniques existantes ou à développer. Pour ce faire, nous avons abordé dans cette thèse, des améliorations à apporter aux méthodologies de test existantes et proposé également des approches de test utilisables en amont de la production des PCBAs (Printed Circuit Board Assemblies) à haute densité et à signaux rapides.Premièrement, nous avons introduit une nouvelle technique sans contact pour tester des PCBAs lorsque l’accès physique de test est très limité. La technique consiste à utiliser des sondes de champ magnétique proche, qui détectent la distribution de champ magnétique émanant de certains composants montés sur le PCB dans le but de tester leur présence sur la carte et leur valeur par la suite. Deuxièmement, une approche de test utilisant des signatures thermiques infrarouges est présentée. Cette technique peut détecter les défauts d’assemblage du composant tel que sa présence, sa valeur et dans certain cas son état de santé, ce qui permet de conclure sur l’état de défaut du PCBA. Afin d’évaluer la pertinence de ces deux techniques, plusieurs scénarios de défaut ont été considérés et analysés avec un algorithme de détection de valeurs aberrantes. Sur plusieurs cas, les défauts de fabrication sont discriminés avec des marges importantes, tout en tenant compte de la variabilité de spécification des composants.Finalement, une technique pour regagner de l’accessibilité de test sur des pistes de transmission de signal de haute fréquence est présentée. La technique consiste à utiliser de petites ouvertures dans le masque de soudure directement au-dessus des pistes portant des signaux digitaux. Les conducteurs exposés sont mis en contact avec une sonde à bout déformable, conducteur et anisotrope. La faisabilité industrielle de cette technique a été testée sur un prototype que nous avions développé en collaboration avec la filiale d’ACTIA Group : ACTIA Engineering ServicesUntil today, the production tests are based mainly on optical verification (AOI), X-ray inspection (AXI), electrical (ICT) and functional tests. Faced with the miniaturization of component packages, the high densification and integration of several technologies (digital, analog, radio frequency, power ...) on the same PCB (Printed Circuit Board), the test techniques listed above are no longer sufficient to fully meet the production test coverage requirements, because they are costly in terms of development time and test cycle and are not very efficient.The objective of this CIFRE thesis with ACTIA Automotive in collaboration with LAAS-CNRS is to define an innovative production test strategy adapted to high-density products. To do this, we have addressed in this work, improvements to existing test methodologies and proposed test approaches usable upstream of the production process of PCBAs (Printed Circuit Board Assemblies).First, we introduced a new contactless technique for testing PCBAs with limited physical test access. The technique involves the use of near-field magnetic sensors, which detect the magnetic signatures from components mounted on the PCB in order to test their presence and their value thereafter. Secondly, a test approach using infrared thermal signatures is presented. This technique can detect component assembly defects such as, presence, value and in some cases its state of health, which allows concluding on the PCBA state of defect. In order to evaluate the relevance of these two techniques, several fault scenarios were considered and analyzed with an outlier detection algorithm. In several cases, the manufacturing defects are discriminated with significant margins, while taking into account the variability in component specifications.Finally, a technique for regaining test accessibility on high frequency signal transmission tracks is presented. The technique uses small openings in the solder mask directly above the tracks carrying digital signals. The exposed conductors are contacted with a probe with deformable and anisotropic conductive tip. The industrial feasibility of this technique was tested on a prototype that we developed in collaboration with the ACTIA Group subsidiary: ACTIA Engineering Services
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Huix, i. Rotllant Miquel. "Noyau de corrélation amélioré pour la réponse linéaire de la théorie de la fonctionnelle de la densité dépendante du temps." Thesis, Grenoble, 2011. http://www.theses.fr/2011GRENV073/document.
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La théorie de la fonctionnelle de la densité dépendante du temps (TDDFT) est une méthode basée sur la densité pour calculer les états excités. Bien que la TDDFT soit une théorie exacte, on doit en pratique partir d'une approximation de la fonctionnelle d'échange-corrélation, qui reste inconnue. L'approximation adiabatique est l'approximation de la fonctionnelle la plus courante. Cette approximation donne de très bons résultats pour les propriétés spectroscopiques, mais elle est inexacte pour les simulations en photochimie. Dans cette thèse, on montre que l'origine du problème réside dans l'approximation de la fonctionnelle de corrélation. Le résultat principal de la thèse consiste en un noyau de corrélation, qui peut être utilisé dans la formulation de la réponse linéaire, noyau dérivée à partir de la théorie des perturbations à plusieurs corps. Le noyau inclut de façon générale les excitations doubles qui donnent l'effet principal à la corrélation dans les états excités. La comparaison de ce noyau avec la fonctionnelle adiabatique nous a permis d'identifier les termes manquants à ce dernier. Nous avons testé la possibilité d'ajouter ces termes comme une correction à l'approximation adiabatique. Le noyau pourrait potentiellement être appliqué à des systèmes de grosse tailleTime-dependent density-functional theory (TDDFT) is a density-functional method for calculating excited states. TDDFT is formally exact, though in practice one has to approximate the unknown exchange-correlation functional, which contains all the unknown many-body effects. The adiabatic functionals are the most commonly used. Although they are very successful for spectroscopy, the adiabatic functionals are too inaccurate to be applied to photochemistry. In this thesis, we show that the main problem is due to the approximations in the correlation functional. The main result of the thesis is a correlation kernel for linear-response TDDFT, derived using many-body perturbation theory techniques, which generally includes double excitations, thus introducing the leading correlation effects in the excited states. The comparison of this kernel with the adiabatic functionals allowed us to identify which correlation effects are missing in these approximation. We tested the possibility of improving the description of correlation by adding the missing terms from many-body theory to the adiabatic functionals. This mixed kernel is more efficient than the full many-body kernel, and can potentially be applied to systems of medium to large size
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Martins, Ana Caroline Vasconcelos. "Explicando Ab Initio a Intensidade de AtivaÃÃo e Antagonismo do Receptor GlutamatÃrgico GluR2." Universidade Federal do CearÃ, 2012. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=8286.
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CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel SuperiorA transmissÃo de impulsos nervosos à feita por meio das sinapses, envolvendo neurotransmissores e receptores. Os receptores ionotrÃpicos glutamatÃrgicos (GluRs) sÃo importantes canais iÃnicos do sistema nervoso central, encontrados em sinapses de excitaÃÃo rÃpida, e estÃo relacionados a funÃÃes cerebrais importantes como aprendizado e memÃria. AlÃm disso, os GluRs tambÃm estÃo associados com certas doenÃas neurolÃgicas e psiquiÃtricas, como por exemplo: a doenÃa de Alzheimer, o mal de Parkinson, a epilepsia, o acidente vascular cerebral, a esclerose lateral amiotrÃfica e a esquizofrenia. Neste trabalho, tiramos vantagem dos dados disponÃveis na literatura da co-cristalizaÃÃo dos seguintes agonistas glutamato (C5H9NO4) e AMPA (C7H10N2O4), do agonista parcial cainato (C10H15NO4) e do antagonista DNQX (C8H2N4O6) com o receptor GluR2 com resoluÃÃo de 1,9 Ã, 1,7 Ã, 1,9 à e 1,8 Ã, respectivamente, para estudar a interaÃÃo destes quatro ligantes com a GluR2 por meio de mÃtodos computacionais ab initio. Os hidrogÃnios ausentes dos dados de difraÃÃo de raios-X foram colocados atravÃs de um processo semi-clÃssico de minimizaÃÃo da energia total GluR2-ligante. A seguir, as simulaÃÃes foram feitas usando a Teoria do Funcional da Densidade (DFT), tanto ao nÃvel da aproximaÃÃo da densidade local (LDA), como da aproximaÃÃo do gradiente generalizado (GGA), para descriÃÃo dos efeitos de troca e correlaÃÃo. A utilizaÃÃo do mÃtodo de fragmentaÃÃo molecular com capas conjugadas (MFCC) tornou possÃvel analisar a interaÃÃo dos ligantes com cada um dos resÃduos prÃximos e pÃs-prÃximos do GluR2. Considerou-se tambÃm a relevÃncia da blindagem dos resÃduos pÃs-prÃximos que interagem com os ligantes, bem como se fez uma anÃlise da energia de interaÃÃo dos resÃduos (prÃximos e pÃs-prÃximos) considerados com os Ãtomos dos ligantes (resultados apresentados nos grÃficos BIRD), sem e com mediaÃÃo das molÃculas de Ãgua existentes no sÃtio de ligaÃÃo (o que permite se determinar ab initio a relevÃncia da Ãgua na energÃtica da interaÃÃo ligante-GluR2). Obteve-se a energia total de interaÃÃo GluR2-ligante em funÃÃo da distÃncia dos centroides dos ligantes aos resÃduos, o que permitiu correlacionÃ-la à intensidade de ativaÃÃo e antagonismo dos neurotransmissores em questÃo. Demonstrou-se que ela segue a ordem AMPA > glutamato > cainato > DNQX somente quando um raio do sÃtio de ligaÃÃo suficientemente grande à considerado, o que explica dados experimentais publicados sobre a ativaÃÃo e antagonismo do receptor glutamatÃrgico GluR2, sugerindo que os resÃduos pÃs-prÃximos podem ser importantes para determinar o funcionamento do receptor. Para o glutamato, os resultados obtidos indicam que os resÃduos atrativos mais relevantes sÃo: Arg485, Lys730 (mediado pela Ãgua W39), Ser654, Leu650 mediado por W69, e Lys656 mediado por W22; os resÃduos repulsivos mais relevantes para o glutamato sÃo Glu402 (pÃs-prÃximo) mediado por W36, Glu657 e Asp651 (pÃs-prÃximos). Para o AMPA os resÃduos atrativos mais relevantes sÃo: Arg485, Thr655 mediado por W134, Lys730 mediado por W137, Lys656 mediado por W138, Lys449 e Arg684 (pÃs-prÃximos); os resÃduos repulsivos mais relevantes para o AMPA sÃo Glu402 mediado por W3, Asp651 mediado por W96 e W139 (pÃs-prÃximo), e Glu657 (pÃs-prÃximo) mediado por W140. Para o cainato os resÃduos atrativos mais relevantes sÃo Arg485, Ser654, Thr655 e Arg684 (pÃs-prÃximo); os resÃduos repulsivos mais relevantes para o Cainato sÃo Glu402, Glu657 mediado por W78 (pÃs-prÃximo) e Asp651. Para o DNQX os resÃduos atrativos mais relevantes sÃo Arg485, Glu705 e Tyr450 mediado por W26 e W137; o resÃduo repulsivo mais relevante para o DNQX à Leu498. Uma plÃiade de perspectivas relacionadas aos resultados obtidos reluz e dentre elas podemos destacar a possibilidade do desenvolvimento de agonistas e antagonistas glutamatÃrgicos com especificidades voltadas à diminuiÃÃo de efeitos colaterais quando utilizados no tratamento de doenÃas relacionadas à neurotransmissÃo glutamatÃrgica.
The transmission of nerve impulses occurs through the synapses, involving neurotransmitters and receptors. The ionotropic glutamate receptors GluRs are important ionic channels of the central nervous system, founded in rapid excitation synapses, and related to important cerebral functions like learning and memory. Besides this, GluRs are also associated with important neurological and psychiatric diseases like Alzheimer, Parkinson, epilepsy, cerebral ischemia, amyotrophic lateral sclerosis, and schizophrenia. In this work, we take advantage of the available data in the literature of co-crystallization of the following full agonists glutamate (C5H9NO4) and AMPA (C7H10N2O4), the partial agonist kainate (C10H15NO4) and the antagonist DNQX (C8H2N4O6) with the GluR2 receptor with resolution of 1.9 Ã, 1.7 Ã, 1.9 Ã and 1.8 Ã, respectively to study the interaction of these four ligands with GluR2 by means of ab initio computational methods. The absent hydrogens in the GluR2-ligand X-ray diffraction data were inserted through a semi-classical total energy minimization process. Next, the simulations were performed within the scope of the Density Functional Theory (DFT), both in the local density approximation (LDA) as generalized gradient approximation (GGA) for the description of exchange-correlation effects. The use of the molecular fragmentation method with conjugated caps (MFCC) allowed to analyze the interaction between the ligands with each one close and next-closed GluR2 residues. It was also considered the relevance of the screening of the next-closed residues with interact with the ligands, and it was performed an analysis of the interaction energy between the focused residues (close and next-closed) with the atoms of the ligands (results depicted in the BIRD panels), without and with the mediation of water molecules existing in the binding pocket (which allows to determine ab initio the relevance of water in the GluR2-ligands energetic). It was obtained the GluR2-ligand total energy interaction as a function of the distance between the ligand centroid and the residues, which allowed to correlate it to the activation strength and antagonism of the ligands focused. It was demonstrated that it follows the order AMPA > glutamate > kainite > DNQX only when a large enough binding pocket radius is taken into account, explaining the experimental data published on the activation and antagonism of the glutamatergic receptor GluR2 and suggesting the next-closed residues can be important to determine the receptor functioning. For the glutamate, the obtained results point that the most important attractive residues are Arg485, Lys730 (water W39 mediated), Ser654, Leu650 (water W69 mediated), and Lys656 (water W22 mediated); the most important repulsive residues for the glutamate are Glu402 (next-closed water W36 mediated), Glu657 and Asp651 (nex-closed). For AMPA, the most important attractive residues are Arg485, Thr655 (water W134 mediated), Lys730 (water W137 mediated), Lys656 (water W138 mediated), Lys449 and Arg684 (next-closed); the most important repulsive residues for AMPA are Glu402 (water W3 mediated), Asp651 (next-closed, water W96 and W139 mediated), and Glu657 (next-closed, water W140 mediated). For kainate the most important attractive residues are Arg485, Ser654, Thr655 and Arg684 (next-closed); the most important repulsive residues for kainite are Glu402, Glu657 (next-closed, water W78 mediated) and Asp651. For DNQX, the most important attractive residues are Arg485, Glu705 and Tyr450 (water W26 and W137 mediated); the most important repulsive residue for DNQX is Leu498. A pleiade of perspectives related with the obtained results shines, among which one can highlight the possibility to develop glutamatergic agonists and antagonists with specificities related to decrease side effects when used in the treatment of maladies related with the glutamatergic neurotransmission.
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Neto, Frederico Ayres de Oliveira. "Propriedades estruturais, eletrônicas e ópticas dos materiais semicondutores \"HgI IND.2\" e \"ZnI IND.2\" e de defeitos em \"HgI IND.2\"." Universidade de São Paulo, 2005. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-05122006-114829/.
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O iodeto de mercúrio em sua fase vermelha, \"alfa\"-\"HgI IND.2, é um material semicondutor que desperta grande interesse tecnológico devido à sua potencial aplicação como detector, a temperatura ambiente, de raios-\"gama\" e X. Sua imediata aplicação como detector de radiação, no entanto, ainda sofre algumas restrições devido às dificuldades de controle sobre a concentração de defeitos pontuais e extensos, durante sua síntese, e sua fácil degradação quando exposto ao ambiente. A presença destes defeitos gera uma redução na mobilidade de portadores de carga, diminuindo a eficiência de detecção. Neste trabalho, realizamos uma investigação teórica das propriedades estruturais, eletrônicas e ópticas do \"alfa\"-\"HgI IND.2\" e do \"ZnI IND.\", cuja estrutura cristalina é análoga à do \"alfa\"-\"HgI IND.2\". Estudamos, também, o comportamento de tais propriedades do material contendo vacâncias de Hg e de I para entendermos o papel desempenhado por estes defeitos nas propriedades do material. Na análise dos resultados, sempre que possível, são apresentadas comparações com outros resultados teóricos e com dados experimentais. Nossos cálculos foram efetuados dentro do formalismo do funcional da densidade em combinação com duas diferentes aproximações para o termo de exchange e correlação. Utilizamos o método Augmented Plane Wave plus local orbitals (APW+lo), que é um método de primeiros princípios e inclui todos os elétrons do sistema (all electron). Adicionalmente, foram utilizados esquemas que incluem efeitos relativísticos e polarização de spin. O estudo dos defeitos foi simulado através do esquema da supercélulaMercuric iodide \"alfa\"-\"HgI IND.2 in its red tetragonal crystalline phase is a semiconducting material of great technological interest due to the potential applications as a detector for y- and X-ray spectroscopy to be operated at room temperatures.
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MACHADO, Camila Maria Benevides. "Configuração absoluta e deslocamentos químicos de moléculas orgânicas por GIAO-DFT." Universidade Federal de Pernambuco, 2016. https://repositorio.ufpe.br/handle/123456789/17507.
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Nesta dissertação, estudamos quatro moléculas quirais através do emprego de quatro funcionais da densidade diferentes com vinte funções de base para encontrar uma combinação que melhor descrevesse o ângulo de rotação óptica destas moléculas. Analisamos também como a ligação de hidrogênio pode influenciar no ângulo de rotação óptica e quais seriam os efeitos dessa ligação de hidrogênio nas propriedades de diferentes sistemas envolvendo compostos nitrogenados cíclicos e ácidos carboxílicos. Os funcionais empregados foram: B3LYP, PBE, PBE0 e ωB97XD; e as funções de base foram: 6-31G, 6-31+G, 6-31++G, 6-31G*, 6-31+G*, 6-31++G*, 6-31G**, 6-31+G**, 6-31++G**, cc-pVDZ, cc-pVTZ, cc-pVQZ, aug-cc-pVDZ, aug-cc-pVTZ, aug-cc-pVQZ, def2-TZVP, def2-TZVPD, def2-TZVPP, def2-TZVPPD e 6-311+G**. As moléculas quirais estudadas para a atribuição da configuração absoluta foram a R,R-dimetiloxirano, S-metiloxirano, S-halotano e (S)(+)4-fenil-2-oxazolidinona. As moléculas estudadas para a espectroscopia de RMN de 1H e cálculos GIAO foram a 1,10-fenantrolina, 2,2-bipiridina, 4,4’-difenil-2,2’-bipiridina e os ácidos carboxílicos: fórmico, acético e benzoico. As geometrias de todas as moléculas e complexos foram otimizadas para que não houvesse nenhuma frequência harmônica imaginária e, a partir delas, o ângulo de rotação óptica foi calculado. Para a molécula (S)(+)4-fenil-2-oxazolidinona, foi observada a possibilidade de formação de dímeros que podem influenciar no valor do ângulo de rotação óptica. As conformações possíveis para esse dímero foram encontradas utilizando mecânica molecular (MMFF - Merck Molecular Force Field) pelo programa SPARTAN 14, tendo suas geometrias sido na sequência otimizadas. As energias de estabilização de todos os complexos foram corrigidas levando em consideração os erros de sobreposição do conjunto de base (BSSE) e da energia do ponto zero (ZPE). O cálculo do ângulo de rotação óptica foi feito com o uso da média de Boltzmann. Todas as moléculas quirais foram estudadas no modo isolado e em clorofórmio através do método PCM. Observamos que moléculas simples, rígidas e sem possibilidade de formação de ligação de hidrogênio, não precisam de funcionais sofisticados para a otimização de sua geometria, mas precisam destes para o cálculo do ângulo de rotação óptica. Para moléculas flexíveis, é necessário um funcional mais sofisticado também para a otimização de geometria. Assim, a melhor combinação de método e base para moléculas mais rígidas para a otimização de geometria foi ωB97XD com a base 6-31G**. Já para moléculas flexíveis, para a otimização de geometria, a melhor base foi def2-TZVP. Em ambos os casos, para o cálculo do ângulo de rotação óptica, a melhor combinação foi ωB97XD com a base def2-TZVP. Para os complexos de ligação de hidrogênio estudados, o deslocamento químico do núcleo do hidrogênio ácido nos complexos envolvendo a 1,10-fenantrolina, como aceitador de elétrons foi mais fortemente afetado em comparação aos complexos correspondentes da 2,2’-bipiridina e 4,4-difenil-2,2’-bipiridina. Os cálculos GIAO estão de acordo com os experimentos de RMN de 1H na previsão da blindagem eletrônica do hidrogênio ácido durante a ligação de hidrogênio existente nos complexos estudados.
In this dissertation, we studied four chiral molecules using four distinct density functionals, and twenty basis functions, searching for a combination that could best describe the optical rotation angle of these molecules. We also analyzed how hydrogen bonding influences the optical rotation angle and what are the effects of hydrogen bonding on the properties of different systems involving cyclic nitrogenated compounds and carboxylic acids. The functionals employed were B3LYP, PBE, PBE0 and ωB97XD. The basis functions employed were: 6-31G, 6-31+G, 6-31++G, 6-31G* 6-31+G*, 6-31++G*, 6-31G**, 6-31+G**, 6-31++G**, cc-pVDZ, cc-pVTZ, cc-pVQZ, aug-cc-pVDZ, aug-cc-pVTZ, aug-cc-pVQZ, def2- TZVP, def2-TZVPD, def2-TZVPP, def2-TZVPPD and 6-311+G**. The chiral molecules studied for the assignment of their absolute configuration were R,R-dimethyloxirane, S-methyl oxirane, S-halothane and (S)(+)4-phenyl-2-oxazolidinone. The molecules studied for the GIAO calculation of 1H NMR spectroscopy were 1,10-phenanthroline, 2,2-bipyridine, 4,4'-diphenyl-2,2'-bipyridine and the carboxylic acids: formic, acetic and benzoic. The geometries of all molecules and complexes were optimized so that there were no imaginary harmonic frequencies and, from them, the optical rotation angle was calculated. For the (S)(+)4-phenyl-2-oxazolidinone molecule, the possibility of dimer formation was observed which can influence the value of the optical rotation angle. The possible conformations for this dimer were found using molecular mechanics by SPARTAN program, and their geometries optimized. The energies of stabilization of all complexes were corrected for the basis set superposition error (BSSE) and zero point energy (ZPE). The calculation of optical rotation angle was made using a Boltzmann average. All chiral molecules were studied, both isolated and in chloroform by the PCM method.We note that simple molecules, rigid and with no possibility of hydrogen bond formation, do not need sophisticated functionals for geometry optimization. However, these sophisticated functionals are indeed needed for the optical rotation angle to be calculated. For flexible molecules, more sophisticated functionals are also necessary for the geometry optimization step. Thus, the best combination method and basis set for the geometry optimization of more rigid molecules found was ωB97XD to the base 6-31G **. As for the geometry optimization of flexible molecules, the best basis set was def2-TZVP. On the other hand, for calculating the optical rotation angle in both cases, the best combination found was ωB97XD with the def2-TZVP.For the hydrogen bonding complexes studied, the chemical shift of the acidic hydrogen nucleus in the complex involving 1,10-phenanthroline as electron acceptor was more strongly affected compared to the corresponding complexes of 2,2'-bipyridine and 4,4'-diphenyl-2,2'-bipyridine. The GIAO calculations agree with the NMR 1H experiments in predicting the electronic shielding of the acidic hydrogen during hydrogen bonding in the studied complexes.
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Fernandez, Nicolas. "Etude des interactions gaz - surface par DFT." Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4715/document.
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Les travaux présentés dans cette thèse relèvent principalement de la réactivité des surfaces et des interactions gaz-surface. Les champs d'application de ce travail sont variés et s'inscrivent principalement dans le domaine de la fusion nucléaire et du projet ITER.Dans ce cadre, la modélisation à l'échelle atomique est un outil important pour comprendre et interpréter les résultats expérimentaux. Notre domaine de compétences est celui du calcul de structures électroniques et des propriétés chimiques. Ces calculs sont principalement conduits dans le cadre de la Théorie de la Fonctionnelle de la Densité (DFT) et de la thermodynamique statistique.Bien que composé de six chapitres, ce manuscrit comporte trois parties principales. La première est dédiée à la présentation des méthodes de calculs utilisées tout au long de cette thèse. La deuxième partie est consacrée à l'étude de la formation du carbure de béryllium à partir d'un dépôt de béryllium sur une surface de graphite. Le degré de fiabilité des résultats DFT a été évalué et les principales étapes de la formation de carbure de béryllium ont été déterminées. La troisième partie développée sur deux chapitres est consacrée à l'étude de l'interaction entre l'hydrogène et le tungstène métallique. La dissolution, la diffusion ainsi que le piégeage de l'hydrogène dans le tungstène ont été étudiés. Un excellent accord a été obtenu entre les valeurs calculées et les résultats expérimentaux de référenceThe work herein presented deals with the reactivity of surfaces and the gas–surface interaction. This work is connected to different fields of applied science and more specifically to the field of nuclear materials for fusion devices like the International Thermonuclear Experimental Reactor (ITER).Numerical simulations at the atomic scale can provide an in depth understanding of the mechanisms at the origin of experimental observations. More specifically, our skills are about electronic structure calculations and chemical properties modelling; most of the work we produced has been conducted within the framework of the Density Functional Theory (DFT) and statistical thermodynamics. While made of six chapters, the manuscript can be cast in three main parts. The first one is dedicated to the methods used throughout this thesis. The second is devoted to the formation of beryllium carbide from deposited beryllium atoms on graphite surfaces; the reliability of the DFT results was benchmarked and the main steps of the beryllium carbide formation were determined. The third part explores the interaction between hydrogen and metallic tungsten. The formation of vacancies in the material, its impact on the solubility and diffusion of hydrogen in tungsten were investigated, and the results were compared with experiment; an excellent agreement was found
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Lövgren, Robin. "Four-component DFT calculations of phosphorescence parameters." Thesis, Linköping University, Computational Physics, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-19180.
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Oscillator strengths and transition energies are calculated for several mono-substitutes of benzene and naphthalene molecules. The substituents investigated are chlorine, bromine and iodine. Calculations for these molecules are presented, at the Hartree-Fock and DFT level of theory. The functional used in DFT is CAM-B3LYP.
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Abella, Guzman Laura. "Computations on Fullerenes: Characterization, Reactivity and Growth." Doctoral thesis, Universitat Rovira i Virgili, 2017. http://hdl.handle.net/10803/460692.
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Aquesta Tesi titulada ‘Computations on Fullerenes: Characterization, Reactivity and Growth’ es focalitza amb els mecanismes de formació i caracterització de ful·lerens prèviament detectats als experiments. Són caixes tancades de carboni formades per hexàgons i dotze pentàgons. Hem col·laborat amb diferents grups experimentals, per tant, ens hem centrat en entendre i racionalitzar els seus experiments. Diferents models de formació de ful·lerens han estat proposats, però encara avui segueix sent un misteri. Els nostres estudis donen completament suport al mecanisme de creixement bottom-up proposat pel Prof. Kroto. Aquest mecanisme ha estat estudiat per càlculs estàtics de DFT i per dinàmica molecular de Car-Parrinello. Una exploració exhaustiva dels isòmers més favorables, així com les superfícies d’energia potencial associades a les insercions d’unitats C2 als ful·lerens i les topologies de les estructures involucrades, han ajudat al desenvolupament d’aquest projecte. Aquest procés d’inserció és exotèrmic/exergònic, i encara que les barreres d’energia lliure són elevades, es poden veure superades a la temperatura de formació de ful·lerens (2000 K). Els isòmers més abundants del Ti@C2n (2n=26-48) i Sc3N@C2n (2n=68-80) s’han relacionat mitjançant unitats C2 i, en alguns casos, alguna isomerització del tipus Stone-Wales. Respecte a la detecció i aïllament dels metal·loful·lerens endoèdrics, ens hem centrat en la seva caracterització. La cloració dels ful·lerens també ha estat estudiada, ja que ha sorgit com una poderosa eina en el món dels derivats de ful·lerens. Famílies de C2n (2n=50,60,66,68,etc.) han estat trobades com cloroful·lerens. Els nostres resultats prediuen que la cloració s’esdevé un cop es formada la caixa neutra a temperatures més baixes de 2000 K, mitjançant l’addició de radical lliure i tenint en compte les distribucions del HOMO i de la densitat d’spin. La majoria dels nostres projectes han estat d’acord amb els resultats experimentals.La Tesis titulada ‘Computations on Fullerenes: Characterization, Reactivity and Growth’ se focaliza con los mecanismos de formación y caracteritzación de fullerenos previamente detectados a los experimentos. Son cajas cerradas de carbono formadas por hexágonos y doce pentágonos. Hemos colaborado con diferentes grupos experimentales, por tanto, nos hemos centrado en entender y racionalizar sus experimentos. Diferentes modelos de formación han sido propuestos, pero todavía hoy sigue siendo un misterio. Nuestros estudios dan soporte al mecanismo de crecimiento bottom-up propuesto por el Prof. Kroto. Este mecanismo ha sido estudiado mediante cálculos estáticos de DFT i por dinámica molecular de Car-Parrinello. Una exploración exhaustiva de los isómeros más favorables, así como las superficies de energía potencial asociadas a las inserciones de unidades C2 a los fullerenos y las topologías de las estructures involucradas, han ayudado al desarrollo de este proyecto. Este proceso de inserción es exotérmico/exergónico, y todavía que las barreras de energía libre son elevadas, se pueden ver superadas a la temperatura de formación de fullerenos (2000 K). Los isómeros más abundantes del Ti@C2n (2n=26-48) y Sc3N@C2n (2n=68-80) se han relacionado mediante unidades C2 y, en algunos casos, alguna isomerización del tipo Stone-Wales. Respecto a la detección y aislamiento de los metallofullerenos endoédricos, nos hemos centrado en su caracteritzación. La cloración de los fullerenos también ha sido estudiada, ya que ha surgido como una poderosa herramienta en el mundo de los derivados de fullerenos. Familias de C2n (2n=50,60,66,68,etc.) han sido encontradas como clorofullerenos. Nuestros resultados predicen que la cloración se forma una vez es formada la caja neutra a temperaturas más bajas de 2000 K, mediante la adición de radical libre y teniendo en cuenta las distribuciones del HOMO y de la densidad de espín. La mayoría de nuestros proyectos han estado de acuerdo con los resultados experimentales.
The Thesis titled ‘Computations on Fullerenes: Characterization, Reactivity and Growth’ is mainly focused on the formation mechanisms and characterization of fullerenes previously detected in experiments. These molecules are closed carbon cages formed by only hexagons and twelve pentagons. Most part of our research has been carried out in collaboration with different experimental groups, therefore we aimed to understand and rationalize their experiments. Although many hypothetical models have been proposed, the fullerene formation mechanism is still a mystery. Our studies rules out the bottom-up mechanism as a model of fullerene formation. We have explored this mechanism by means of static DFT and Car-Parrinello molecular dynamics calculations for series of different endohedral fullerenes. A comprehensive exploration of the most favourable isomers, potential energy surfaces associated with the successive C2 insertions and topologies of the involved structures, helped us to develop this project. The insertion of a C2 unit to already formed EMF is always an exothermic/exergonic process, and the free energy barriers for each step are attainable at temperature of fullerene formation (2000 K). The most abundant isomers of Ti@C2n (2n=26-48) and Sc3N@C2n (2n=68-80) are formally linked by direct C2 insertions and in a few cases by additional Stone-Wales transformations. Regarding the detection and isolation of endohedral metallofullerenes let us to perform a computational study of the rationalization and characterization of these isomers. Chlorination has emerged as a powerful tool in fullerene derivatives. Several C2n families (2n=50,60,66,68,etc.) have been found to show cages exohedrally chlorinated. According to our results, chlorination would take place at a temperature significantly lower than 2000 K by free radical addition considering the HOMO and the spin density distributions of the pristine cage and intermediates, once the lowest energy neutral isomers are formed. Most of our projects resulted in suitable and in agreement with experiments.
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Barthel, Robert. "Growth of unsaturated, cyclic, and polycyclic aromatic hydrocarbons: Reactions under the conditions of the interstellar medium." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2009. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1238024025498-21465.
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Hydrocarbons, in particular polycyclic aromatic hydrocarbons (PAHs), have been long discussed to be carriers of interstellar infrared (IR) emission and ultraviolet (UV) absorption features. Yet, their origin in dense phases of the interstellar medium (ISM), such as molecular clouds, remains unclear. In this work, growth mechanisms based on ion-molecule reactions between cationic PAHs/hydrocarbons and methyne (CH) were investigated. The reaction type and the precursor were derived and selected from known chemical and physical properties of the ISM. These chemical reactions were characterised by calculating branching ratios (based on cross sections) and capture rate coefficients, minimum reaction paths, reaction enthalpies, thermal equilibrium constants, and microcanonic isomerisation and radiative deactivation rate coefficients. In order to cope with the variety of reaction parameters, a hierarchic workflow scheme was set up. First, the reaction potential energy surface was sampled by molecular dynamics simulations. Then, minimum energy paths of the most probable reaction channels were investigated. Finally, molecular and kinetic properties of stationary points were calculated. The quantum chemical level of theory was increased at each step from DFTB (tight-binding density-functional), to DFT, and finally to post-Hartree-Fock methods. Results on CH based hydrocarbon growth showed the transition from non-cyclic hydrocarbons to cyclic and aromatic structures and from cyclic to polycyclic aromatic hydrocarbons. Additionally, the reactive collisions between hydrocarbons and CH were found to produce sufficient energy for isomerisation and fragmentation processes even at ultra low temperatures. In all, the results indicate that methyne might be a proper precursor for the formation of large interstellar PAHsKohlenwasserstoffe, insbesondere polyzyklische Kohlenwasserstoffe (engl. PAHs), werden seit einigen Jahren als Mitverursacher interstellar IR-Emissions- und UV-Absorptionsbanden angesehen und diskutiert. Dabei ist die Herkunft dieser Moleküle in den dichten Phasen des interstellaren Mediums (ISM) aber noch nicht aufgeklärt. In dieser Arbeit wurden daher die Bildungsmechanismen, welche auf Ion-Molekül-Reaktionen zwischen kationischen PAHs und Kohlenwasserstoffen und dem Molekül CH beruhen, untersucht. Sowohl der Reaktionstyp als auch der Präkursor wurden anhand von bekannten physikalischen und chemischen Eigenschaften des ISM abgeleitet und ausgewählt. Die Analyse der chemischen Reaktionen basierte auf Berechnungen zur Produktzusammensetzung und Einfangsratenkoeffizienten (welche wiederum aus berechneten Reaktionsquerschnitten hervorgingen) Minimumenergiepfade (MEP), Reaktionsenthalpien, thermische Gleichgewichtskonstanten und mikrokanonische Isomerisierungs- und Strahlungsdeaktivierungs-Ratenkoeffizienten. Um der Vielzahl an Reaktionsparameter gerecht zu werden, wurden die Berechnungsmethoden entsprechend eines hierarischen Fließschemas kombiniert. Hierzu wurden zuerst durch Molekulardynamik-Simulationen die Reaktionspotentialenergieflächen abgerastert. Auf der nächsten Stufe wurden statistisch bedeutsame Reaktionskanäle bezüglich ihrer Minimumenergiepfade untersucht. Den Abschluss bildete die Berechnung molekularer und kinetischer Charakteristika stationärer Punkte auf einem MEP. Entsprechend dieses Schemas wurde die quantenchemische Genauigkeit auf jeder Stufe von approximativer DFT über DFT zu post-Hartree-Fock verändert. Die Ergebnisse des CH-basierten Kohlenwasserstoffwachstums zeigten einen Übergang von nichtzyklischen zu zyklischen and aromatischen Strukturen, sowie von zyklischen zu polyzyklischen Kohlenwasserstoffen. Außerdem zeigte sich, dass reaktive Kollisionen zwischen Kohlenwasserstoffen und CH auch bei Tiefsttemperaturen immer ausreichend Energie für Isomerisierungs- und Fragmentationsprozesse liefert. Die Ergebnisse dieser Arbeit lassen den Schluss zu, dass CH ein geeigneter Präkursor für die Bildung großer interstellarer PAH ist
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Miroshnichenko, O. (Olga). "Properties of binary oxides:a DFT study." Doctoral thesis, Oulun yliopisto, 2019. http://urn.fi/urn:isbn:9789526223018.
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Abstract Titanium dioxide nanoparticles are used in an enormous amount of applications. Their properties are different from bulk TiO₂ and are affected by adsorbates that are unavoidably present on the surface. In this thesis, the effect of OH and SO₄ groups (the adsorbants present on the surface during manufacturing) on the properties of anatase-structured TiO₂ nanoparticles is studied. It was found that the above mentioned groups change both the geometric and electronic structure of nanoparticles, resulting in changes in the photoabsorption spectrum. Bader charges are calculated using electron density from Density Functional Theory calculations. They can be used for determination of the oxidation state of the atom. The relation between computed partial charges and oxidation states for binary oxides using data from open materials database has been demonstrated in this work using a linear regression. The applicability of the oxidation state determination by Bader charges for mixed valence compounds and surfaces is consideredTiivistelmä Titaanidioksidinanopartikkeleita käytetään lukuisissa sovelluksissa. Niiden ominaisuudet poikkeavat kiinteän TiO₂:n ominaisuuksista, ja niihin vaikuttavat pinnalle väistämättä absorboituvat aineet. Tässä työssä on tutkittu OH- ja SO₄-ryhmien vaikutusta anataasirakenteisten TiO₂-nanopartikkelien ominaisuuksiin. Tällaisia ryhmiä esiintyy yleisesti nanopartikkelien pinnalla valmistusprosessien aikana. Työssä havaittiin, että nämä ryhmät muuttavat nanopartikkelien rakenteellisia ja sähköisiä ominaisuuksia, ja siten vaikuttavat myös fotoabsorptiospektriin. Baderin varaukset voidaan laskea käyttäen tiheysfunktionaaliteoriaan perustuvista laskuista saatavaa elektronitiheyttä. Niitä voidaan käyttää atomin hapetustilan laskemiseen. Tässä työssä on osoitettu, että binääristen oksidien tapauksessa laskettujen osittaisvarauksien ja hapetustilan välillä on yhteys. Tämä yhteys voitiin osoittaa käyttämällä lineaarista regressiota. Työssä tarkastellaan myös menetelmän soveltuvuutta hapetustilojen määrittämiseen sekavalenssiyhdisteille ja pinnoille
Original papers Original publications are not included in the electronic version of the dissertation. Miroshnichenko O., Auvinen S., & Alatalo M. (2015). A DFT study of the effect of OH groups on the optical, electronic, and structural properties of TiO₂ nanoparticles. Phys. Chem. Chem. Phys., 17, 5321–5327. https://doi.org/10.1039/c4cp02789b Miroshnichenko O., Posysaev S., & Alatalo M. (2016). A DFT study of the effect of SO4 groups on the properties of TiO₂ nanoparticles. Phys. Chem. Chem. Phys., 18, 33068–33076. https://doi.org/10.1039/c6cp05681d http://jultika.oulu.fi/Record/nbnfi-fe201707037608 Posysaev S., Miroshnichenko O., Alatalo M., Le D., & Rahman T.S. (2019). Oxidation states of binary oxides from data analytics of the electronic structure. Comput. Mater. Sci., 161, 403–414. https://doi.org/10.1016/j.commatsci.2019.01.046
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Ghanmi, Nour El Houda. "Etude DFT de l'influence des ions fluorure sur les mécanismes de croissance des oxydes nanoporeux par oxydation anodique." Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066354/document.
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Des films nanoporeux de dioxyde de titane peuvent être formés au-dessus d’un substrat de titane par oxydation anodique, c’est-à-dire lorsque le métal est plongé dans un électrolyte fluoré et est soumis à une tension ou une densité de courant constante. Le dopage par des ions fluorures permet également d’améliorer les propriétés photocatalytiques de TiO2 utiles pour de nombreuses applications. L’objectif de cette thèse consiste à étudier, par la théorie de la fonctionnelle de la densité (DFT), l’influence des ions fluorures sur les mécanismes élémentaires ayant lieu lors de la croissance des couches de TiO2. Nous nous attacherons notamment à comprendre l’influence de la phase et de l’orientation cristallographique des surfaces de TiO2 fluoré, sur leurs stabilités et leurs propriétés photocatalytiques. Tous les calculs DFT ont été effectués avec le logiciel VASP qui permet de simuler des systèmes périodiques. Dans un premier temps, nous avons étudié l’adsorption de F et de F2 sur différentes surfaces de TiO2 parfaites et défectueuses. Deux groupes de surfaces ont pu être distingués vis-à-vis de leur réactivité et de leurs propriétés. Nous nous sommes ensuite intéressés au F-dopage à et sous différentes surfaces. Cette étude est inédite car le dopage a été essentiellement étudié au niveau du massif de TiO2. L’influence de l’hydroxylation des surfaces sur la réactivité de TiO2 vis-à-vis du fluor a été étudié afin d’obtenir des informations sur la croissance des couches d’oxydeNanoporous titanium dioxide films can be formed over a titanium substrate by anodic oxidation, ie, when the metal is immersed in a fluorinated electrolyte and a constant voltage or a current density is applied. Doping with fluoride ions also improve the photocatalytic properties of TiO2 which is crucial for many applications. The goal of this thesis is to study the influence of fluoride ions on the elementary mechanisms during the growth of the TiO2 layers by the density functional theory (DFT). In particular, we will try to understand the influence of the phase and the crystallographic orientation of fluorinated TiO2 surfaces on their stability and their photocatalytic properties. All DFT calculations were carried out using VASP software which allows to simulate periodic systems. In a first step, we studied the adsorption of F and F2 on different perfect and defective TiO2 surfaces. Two groups of surfaces have been distinguished from their reactivity and their properties. Then we focused on F-doping at and under different surfaces. This study is pioneering because F-doping was mainly studied in bulk TiO2. The influence of surface hydroxylation on the reactivity of TiO2 towards fluoride ions has been studied in order to obtain information on the growth of the oxide layers
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Nguyen, Van Bac. "Prédiction des morphologies de nanoparticules métalliques à partir de calculs DFT des interactions surface-ligand." Thesis, Toulouse 3, 2016. http://www.theses.fr/2016TOU30299/document.
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Les nanoparticules (NPs) sont des matériaux fonctionnels importants du fait de leur taille nanométrique. Cette réduction en taille, associée à la composition, à l'orientation des surfaces et à la morphologie contribue à l'exaltation de nombreuses propriétés importantes telles que les propriétés électroniques, magnétiques, catalytiques, optiques, etc. Pour contrôler la morphologie des NPs, de nombreux efforts ont été consacrés à comprendre leurs mécanismes de formation et l'origine de leur stabilité. Parmi les nanoparticules métalliques, le cobalt, avec sa structure hexagonale compact (hcp), est particulièrement intéressant pour la possibilité d'obtenir des nanocristaux de forme "naturellement" anisotropique. Par synthèse chimique en milieu liquide, des NPs de différentes morphologies telles que des disques, des plaques, des bâtonnets, des fils et des cubes ont été obtenues en contrôlant le type de précurseur, de l'agent réducteur, des ligands stabilisants, ainsi que la concentration de ces ligands, la température ou la vitesse d'injection des précurseurs. Même si ces conditions de synthèse ont été rationalisées, les mécanismes à l'origine de ces différentes morphologies ne sont pas encore bien connus. Dans ce travail, nous avons développé deux modèles quantitatifs pour la prédiction de la morphologie, l'un est basé sur l'équilibre thermodynamique de l'état final, et l'autre sur un contrôle par l'effet cinétique. Pour appliquer ces modèles, il a été nécessaire de calculer dans un premier temps, avec la théorie de la fonctionnelle de la densité (DFT), les comportements d'adsorption des molécules ligands en fonction du taux de recouvrement sur les facettes de différentes orientations du métal. Pour ce faire, l'adsorption des ligands CH 3 NH 2 , CH 3 COO, C 5 H 11 COO et C 11 H 23 COO a été modélisée sur les différentes surfaces de Co et de Ni. La morphologie des NPs de Co prédite par ces deux modèles a été comparée à celles obtenues expérimentalement et à d'autres résultats théoriques de la littérature. La variété des formes obtenues par le modèle cinétique semblerait mieux correspondre aux NPs synthétisées avec les différentes conditions expérimentales. Ceci confirme que la morphologie des NPs est guidée avant tout par un effet cinétiqueNanoparticles are one of the most important families of functional materials due to their nanometric size. This size reduction, associated to their composition, surfaces orientation and morphology has contributed to the emergence of new important properties such as electronic, magnetic, catalytic, optic, etc. To control the morphology of NPs, many efforts have been devoted to understand their formation mechanism and the origin of their stability. Among metallic nanoparticles, cobalt, with its hexagonal closed-packed (hcp) structure, is particularly interesting because of the possibility to grow "naturally" anisotropic shaped nanocrystals. Using chemical synthesis in liquid environment, various morphologies such as disks, plates, rods, wires and cubes have been obtained by controlling the precursor type, the reducing agent, the stabilizing ligands as well as their concentration, the temperature or the rate of precursor injection. Even if these synthesis conditions have been rationalized, few is known concerning the growth mechanisms at the atomic scale. In this work, we have developed two quantitative morphology prediction models, one based on the final thermodynamic equilibrium state, while another is controlled by the kinetics. These models require the knowledge of the adsorption behaviors of stabilizing molecules as a function of surface coverage on preferential facets of NPs. To this end, density functional theory (DFT) calculations were performed on a series of stabilizing molecules (CH3NH2 , CH3COO C5H11OO and C11H23COO) adsorbed on the different Co and Ni surfaces. The shape of the Co NPs obtained by these two models was compared to experimental morphologies and other theoretical results from the literature. The variety of forms predicted by the kinetic model agrees better with the NPs morphologies obtained under the different synthesis conditions. This confirms that the morphology control of NPs is mostly driven by the kinetics
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Oliveira, Arquimedes Maia de. "Synthesis, characterization and reactivity study of the complexes cis-[Ru(bpy)2(TU)(H2O)](PF6)2 E cis-[Ru(bpy)2(TU)(NO)](PF6)3." Universidade Federal do CearÃ, 2009. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=3987.
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Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgicoNeste trabalho foi realizada a sÃntese e a caracterizaÃÃo dos complexos cis-[Ru(bpy)2(TU)(H2O)](PF6)2 e cis-[Ru(bpy)2(TU)(NO)](PF6)3, onde TU=TiourÃia e bpy= 2,2â-bipiridina, bem como os estudos preliminares relacionados a reatividade do nitrosilo-complexo frente a luz branca e na presenÃa do redutor biolÃgico cisteÃna. O aquo-complexo possui o ligante TiourÃia coordenado ao centro metÃlico via Ãtomo de enxofre, tendo em vista os dados obtidos por espectroscopia vibracional na regiÃo do infravermelho bem como aqueles calculados por DFT. O complexo apresentou um potencial de meia-onda (E1/2) referente ao par redox RuIII/II em 415 mV vs Ag|AgCl e um espectro eletrÃnico dependente do pH devido ao equilÃbrio de deprotonaÃÃo do hidrogÃnio do grupo NH2 da TiourÃia que ocorre com pKa = 10,11. O nitrosilo-complexo, que tambÃm possui o ligante TiourÃia coordenado ao centro metÃlico via Ãtomo de enxofre, apresentou um valor correspondente a frequÃncia de estiramento NO em 1932 cm-1, coerente com o valor do potencial de meia-onda (E1/2) referente ao par redox NO+/0 em 37,5 mV, com o valor obtido para a constante de equilÃbrio relacionada a reaÃÃo de inter-conversÃo nitrosil-complexo/nitro-complexo, K = 1,26 x 1015, e com os valores calculados por DFT para a energia do orbital LUMO e da carga parcial sobre o ligante nitrosil. O nitrosilo-complexo apresentou uma boa reatividade em relaÃÃo à liberaÃÃo de NO0 tanto por reduÃÃo eletroquÃmica quanto por reduÃÃo fotoquÃmica, porÃm o mecanismo em que ocorre esta liberaÃÃo no que se refere à fotoquÃmica se dà de uma forma diferenciada em relaÃÃo a sistemas similares da literatura. O mecanismo de liberaÃÃo do NO0 a partir do nitrosilo-complexo apÃs reaÃÃo com o redutor biolÃgico cisteÃna, tambÃm parece ocorrer de forma diferenciada em relaÃÃo a sistemas similares jà estudados.
In this work, it was carried out the synthesis and characterization of the complexes cis-[Ru(bpy) 2 (TU)(H 2 O)](PF 6 ) 2 and cis - [Ru(bpy) 2 (TU)(NO)](PF 6 ) 3 , where TU = thiourea and bpy = 2,2 ' - bipyridine, and preliminary studies of the photoreactivity of the nitrosyl complex and its reaction with cysteine, a biological reductant agent. The aqua - complex contains the thiourea ligand coordinated to the metal center through the sulfur atom, according to the data obtained by infrared vibrational spectroscopy and reinforced by theoretical study using DFT. The complex showed a half -wave potential (E1/2) for the RuIII/II redox couple at 415 mV vs Ag | AgCl and a p H-dependent electronic spectrum, due to acid - base equilibrium of the proton released from the NH 2 group of thiourea that presents a pKa = 10.11. The nitrosyl complex, which also contains the thiourea ligand coordinated to the metal center through the sulf ur atom, showed NO stretching frequency at 1932 cm - 1 , which is also consistent with the half - wave potential (E 1/2 ) for the NO +/0 redox couple at 37.5 mV. Additionally, it was measured the equilibrium constant for the inter - conversion reaction of nitrosyl to nitro complex at K = 1.26 x 10 15 . These data were further supported by empirical calculations carried out by DFT, where the en ergy of the LUMO orbital and the electronic density on the nitrosyl ligand were in agreement with the previous data. The nitrosyl complex has exhibited efficient release of NO in solution whether upon electrochemical or photochemical reduction. Curiously, the mechanism for the photochemical release of NO was different from other similar complexes. The chemical reduction of the nitrosyl complex with cysteine has efficiently released NO but again it followed a different mechanism from that found in other rel ated systems.
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Tang, Miru. "DENSITY FUNCTIONAL THEORY STUDIES ON THE STRUCTURE AND CATALYTIC ACTIVITY OF METAL OXIDES." OpenSIUC, 2018. https://opensiuc.lib.siu.edu/dissertations/1602.
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In this dissertation, I present four projects on the fundamental study of the surface configurations and reactivity of the metal oxides using density functional theory computational method. In the first project, we studied the formaldehyde adsorption and diffusion on rutile TiO2 (110) surface. By comparing the adsorption of formaldehyde on stoichiometric and defective TiO2 surfaces under the same condition, we evaluated the effect of surface oxygen vacancy on their interaction with formaldehyde. The project involved close collaboration with Dr. Zhenrong Zhang’s group of Baylor University who studied the formaldehyde chemistry on rutile TiO2(110) surface using a combination of STM and other surface science techniques. In the second project, we compared the surface chemistries of formaldehyde and formic acid on rutile TiO2 and SnO2, two structurally similar but chemically different oxides. We analyzed the oxidation of formaldehyde to formic acid on two oxides and assessed the role of surface oxygen in the oxidation. In the third project, we studied the oxygen evolution reaction (OER) catalyzed by γ-FeOOH (010) under the alkaline condition. The OER process was divided into four elementary steps and the potential energy profiles of these steps on three terminations of the γ-FeOOH (010) surface were mapped out. Based on the computed reaction energies, we determined the most probable OER reaction pathway on each surface termination. We found that partially exposed surface Fe sites were the active sites for the OER process. In the fourth project, we studied the potential of iron oxides (FeOx) and iron-titanium mixed oxides (FeTiOx) as solid oxygen carriers for the chemical looping combustion (CLC) process. As oxygen carriers for CLC, FeOx and FeTiOx in fully oxidized forms went through a series of reduction steps by reacting with the fuel molecules. The reduced oxides were then re-oxidized in an air reactor to restore their oxygen. By studying the surface oxygen vacancy formation and oxygen diffusion, we gained insights into the initial stage of reduction process and activities of FeOx and FeTiOx as well as the effect of Ti on oxygen carrying properties of FeTiOx for CLC.
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Garduño, Jiménez Juan Carlos. "ANÁLISIS TEÓRICO DE LA FORMACIÓN DE PUENTES DISULFURO VECINALES." Tesis de Licenciatura, Universidad Autónoma del Estado de México, 2017. http://hdl.handle.net/20.500.11799/80119.
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La cisteína es fundamental para la estabilidad y el plegamiento de las proteínas, de igual manera ayuda a la interacción entre proteínas y metales, catálisis enzimática asi como la regulación de la actividad biológica de las proteínas, mediante la formación de puentes disulfuro aprovechando propiedades redox del par tiol-disulfuro. Estos se encargan de regular alteraciones en el organismo como el envejecimiento celular y el desarrollo de enfermedades, afectando ciclos celulares y procesos como la coagulación de la sangre, control de epítopes, uniones a zinc, etc. En las bacterias y virus se emplean como llaves de entrada o salida de un compartimento celular a otro.
En el presente trabajo se tiene la finalidad se realizar una investigación para tratar de comprender la formación de puentes disulfuro vecinales prohibidos por medio de la química computacional empleando Teoría de Funcionales de la Densidad (DFT, por sus siglas en ingles). Se estudiará la reacción tioles-disulfuro, estudiando los parámetros de las energías potenciales, energías de reacción e índices de reactividad.Proyecto LANCAD
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Barthel, Robert. "Growth of unsaturated, cyclic, and polycyclic aromatic hydrocarbons: Reactions under the conditions of the interstellar medium." Doctoral thesis, Technische Universität Dresden, 2008. https://tud.qucosa.de/id/qucosa%3A23589.
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Hydrocarbons, in particular polycyclic aromatic hydrocarbons (PAHs), have been long discussed to be carriers of interstellar infrared (IR) emission and ultraviolet (UV) absorption features. Yet, their origin in dense phases of the interstellar medium (ISM), such as molecular clouds, remains unclear. In this work, growth mechanisms based on ion-molecule reactions between cationic PAHs/hydrocarbons and methyne (CH) were investigated. The reaction type and the precursor were derived and selected from known chemical and physical properties of the ISM. These chemical reactions were characterised by calculating branching ratios (based on cross sections) and capture rate coefficients, minimum reaction paths, reaction enthalpies, thermal equilibrium constants, and microcanonic isomerisation and radiative deactivation rate coefficients. In order to cope with the variety of reaction parameters, a hierarchic workflow scheme was set up. First, the reaction potential energy surface was sampled by molecular dynamics simulations. Then, minimum energy paths of the most probable reaction channels were investigated. Finally, molecular and kinetic properties of stationary points were calculated. The quantum chemical level of theory was increased at each step from DFTB (tight-binding density-functional), to DFT, and finally to post-Hartree-Fock methods. Results on CH based hydrocarbon growth showed the transition from non-cyclic hydrocarbons to cyclic and aromatic structures and from cyclic to polycyclic aromatic hydrocarbons. Additionally, the reactive collisions between hydrocarbons and CH were found to produce sufficient energy for isomerisation and fragmentation processes even at ultra low temperatures. In all, the results indicate that methyne might be a proper precursor for the formation of large interstellar PAHs.Kohlenwasserstoffe, insbesondere polyzyklische Kohlenwasserstoffe (engl. PAHs), werden seit einigen Jahren als Mitverursacher interstellar IR-Emissions- und UV-Absorptionsbanden angesehen und diskutiert. Dabei ist die Herkunft dieser Moleküle in den dichten Phasen des interstellaren Mediums (ISM) aber noch nicht aufgeklärt. In dieser Arbeit wurden daher die Bildungsmechanismen, welche auf Ion-Molekül-Reaktionen zwischen kationischen PAHs und Kohlenwasserstoffen und dem Molekül CH beruhen, untersucht. Sowohl der Reaktionstyp als auch der Präkursor wurden anhand von bekannten physikalischen und chemischen Eigenschaften des ISM abgeleitet und ausgewählt. Die Analyse der chemischen Reaktionen basierte auf Berechnungen zur Produktzusammensetzung und Einfangsratenkoeffizienten (welche wiederum aus berechneten Reaktionsquerschnitten hervorgingen) Minimumenergiepfade (MEP), Reaktionsenthalpien, thermische Gleichgewichtskonstanten und mikrokanonische Isomerisierungs- und Strahlungsdeaktivierungs-Ratenkoeffizienten. Um der Vielzahl an Reaktionsparameter gerecht zu werden, wurden die Berechnungsmethoden entsprechend eines hierarischen Fließschemas kombiniert. Hierzu wurden zuerst durch Molekulardynamik-Simulationen die Reaktionspotentialenergieflächen abgerastert. Auf der nächsten Stufe wurden statistisch bedeutsame Reaktionskanäle bezüglich ihrer Minimumenergiepfade untersucht. Den Abschluss bildete die Berechnung molekularer und kinetischer Charakteristika stationärer Punkte auf einem MEP. Entsprechend dieses Schemas wurde die quantenchemische Genauigkeit auf jeder Stufe von approximativer DFT über DFT zu post-Hartree-Fock verändert. Die Ergebnisse des CH-basierten Kohlenwasserstoffwachstums zeigten einen Übergang von nichtzyklischen zu zyklischen and aromatischen Strukturen, sowie von zyklischen zu polyzyklischen Kohlenwasserstoffen. Außerdem zeigte sich, dass reaktive Kollisionen zwischen Kohlenwasserstoffen und CH auch bei Tiefsttemperaturen immer ausreichend Energie für Isomerisierungs- und Fragmentationsprozesse liefert. Die Ergebnisse dieser Arbeit lassen den Schluss zu, dass CH ein geeigneter Präkursor für die Bildung großer interstellarer PAH ist.
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Pereira, Arquimedes Mariano. "Ligação de hidrogênio intermolecular entre CL3CH E F3CH e as espécies receptoras de próton: C2H2, C2H4, C3H4, C3H6 E C4H4." Universidade Federal da Paraíba, 2016. http://tede.biblioteca.ufpb.br:8080/handle/tede/9207.
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Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq
This work deals with the computational quantum study of structural, electronic, vibrational, hyperconjugative and topological of hydrogen complexes with Cl3CH and F3CH donors, with the aceptor species proton, C2H2, C2H4, C3H4, C3H6 and C4H4, interacting with a region high electron density of the type π and pseudo-π. The computational methods used electronic structure were Density Functional Theory with functional hybrids B3LYP and X3LYP with Perturbative and Theory of many bodies of order 2, with a series of bases. The amounts of hydrogen bond energy suffered superposition error corrections of the Basic Feature Set and Vibrational Zero Point Energy. The complexes of hydrogen with the donor Cl3CH showed increases in the length of the C-H bond, while the present F3CH shortening of the C-H bond length due to formation of intermolecular bond. This trend is found for the deviation in the infrared spectrum, Chloroform has red shift while Fluoroform has blue shift deviations. The use of quantum theory of atoms in molecules shows the change in electron density of both interacting species, and in addition the density values are small and the Laplacian are positive. The methods followed the same trend for the properties of interest, suggesting the use of calculations via density functional theory, due to lower computational demand to study such systems.
Este trabalho trata do estudo quântico computacional de propriedades estruturais, eletrônicas, vibracionais, hiperconjugativas e topológicas dos complexos de hidrogênio com doadores Cl3CH e F3CH, com as espécies receptoras de próton, C2H2, C2H4, C3H4, C3H6 e C4H4, interagindo com uma região de alta densidade eletrônica do tipo π e pseudo- π. Os métodos computacionais de estrutura eletrônica empregados foram a Teoria do Funcional da Densidade com os funcionais híbridos B3LYP e X3LYP e a Teoria Perturbativa de Muitos Corpos de ordem 2, com uma série de bases. Os valores da energia da ligação de hidrogênio sofreram correções do Erro de Superposição do Conjunto de Funções de Base e da Energia Vibracional do Ponto Zero. Os complexos de hidrogênio com o doador Cl3CH apresentaram incrementos no comprimento da ligação C-H, enquanto o F3CH apresentam encurtamento do comprimento de ligação H-C, devido a formação da ligação intermolecular. Essa tendência é encontrada para o desvio no espectro infravermelho, o Clorofórmio apresenta red shift enquanto o Fluorfórmio tem desvios blue shift. O emprego da teoria quântica de átomos em moléculas evidencia a mudança na densidade eletrônica de ambas as espécies interagentes, e, além disso os valores da densidade são pequenos e do laplaciano da densidade são positivos. Os métodos empregados seguiram a mesma tendência para as propriedades de interesse, sugerindo o uso de cálculos via teoria do funcional da densidade, devido a menor demanda computacional, para estudar sistemas desse tipo. Palavras-Chave: Ligação de Hidrogênio Intermolecular, DFT/B3LYP, DFT/X3LYP, MP2 e QTAIM.
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Ponnuchamy, Veerapandian. "Towards A Better Understanding of Lithium Ion Local Environment in Pure, Binary and Ternary Mixtures of Carbonate Solvents : A Numerical Approach." Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GRENY004/document.
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En raison de l'augmentation de la demande d'énergie, ressources écologiques respectueux de l'environnement et durables (solaires, éoliennes) doivent être développées afin de remplacer les combustibles fossiles. Ces sources d'énergie sont discontinues, étant corrélés avec les conditions météorologiques et leur disponibilité est fluctuant dans le temps. En conséquence, les dispositifs de stockage d'énergie à grande échelle sont devenus incontournables, pour stocker l'énergie sur des échelles de temps longues avec une bonne compatibilité environnementale. La conversion d'énergie électrochimique est le mécanisme clé pour les développements technologiques des sources d'énergie alternatives. Parmi ces systèmes, les batteries Lithium-ion (LIB) ont démontré être les plus robustes et efficaces et sont devenus la technologie courante pour les systèmes de stockage d'énergie de haute performance. Ils sont largement utilisés comme sources d'énergie primaire pour des applications populaires (ordinateurs portables, téléphones cellulaires, et autres). La LIB typique est constitué de deux électrodes, séparés par un électrolyte. Celui-ci joue un rôle très important dans le transfert des ions entre les électrodes fournissant la courante électrique. Ce travail de thèse porte sur les matériaux complexes utilisés comme électrolytes dans les LIB, qui ont un impact sur les propriétés de transport du ion Li et les performances électrochimiques. Habituellement l'électrolyte est constitué de sels de Li et de mélanges de solvants organiques, tels que les carbonates cycliques ou linéaires. Il est donc indispensable de clarifier les propriétés structurelles les plus importantes, et leurs implications sur le transport des ions Li+ dans des solvants purs et mixtes. Nous avons effectué une étude théorique basée sur la théorie du fonctionnelle densité (DFT) et la dynamique moléculaire (MD), et nous avons consideré des carbonates cyclique (carbonate d'éthylène, EC, et carbonate de propylène, PC) et le carbonate de diméthyle, DMC, linéaire. Les calculs DFT ont fourni une image détaillée des structures optimisées de molécules de carbonate et le ion Li+, y compris les groupes pures Li+(S)n (S =EC,PC,DMC et n=1-5), groupes mixtes binaires, Li+(S1)m(S2)n (S1,S2=EC,PC,DMC, m+n=4), et ternaires Li+(EC)l(DMC)m(PC)n (l+m+n=4). L'effet de l'anion PF6 a également été étudié. Nous avons aussi étudié la structure de la couche de coordination autour du Li+, dans tous les cas. Nos résultats montrent que les complexes Li+(EC)4, Li+(DMC)4 et Li+(PC)3 sont les plus stables, selon les valeurs de l'énergie libre de Gibbs, en accord avec les études précédentes. Les énergies libres de réactions calculés pour les mélanges binaires suggèrent que l'ajout de molécules EC et PC aux clusters Li+ -DMC sont plus favorables que l'addition de DMC aux amas Li+-EC et Li+-PC. Dans la plupart des cas, la substitution de solvant aux mélanges binaires sont défavorables. Dans le cas de mélanges ternaires, la molécule DMC ne peut pas remplacer EC et PC, tandis que PC peut facilement remplacer EC et DMC. Notre étude montre que PC tend à substituer EC dans la couche de solvation. Nous avons complété nos études ab-initio par des simulations MD d'une ion Li immergé dans les solvants purs et dans des mélanges de solvants d'intérêt pour les batteries, EC:DMC(1: 1) et EC:DMC:PC(1:1:3). MD est un outil très puissant et nous a permis de clarifier la pertinence des structures découvertes par DFT lorsque le ion est entouré par des solvants mélangés. En effet,la DFT fournit des informations sur les structures les plus stables de groupes isolés, mais aucune information sur leur stabilité ou de la multiplicité (entropie) lorsqu'il est immergé dans un environnement solvant infinie. Les données MD, ainsi que les calculs DFT nous ont permis de donner une image très complète de la structure locale de mélanges de solvants autour le ion lithium, sensiblement amélioré par rapport aux travaux précédentsDue to the increasing global energy demand, eco-friendly and sustainable green resources including solar, or wind energies must be developed, in order to replace fossil fuels. These sources of energy are unfortunately discontinuous, being correlated with weather conditions and their availability is therefore strongly fluctuating in time. As a consequence, large-scale energy storage devices have become fundamental, to store energy on long time scales with a good environmental compatibility. Electrochemical energy conversion is the key mechanism for alternative power sources technological developments. Among these systems, Lithium-ion (Li+) batteries (LIBs) have demonstrated to be the most robust and efficient, and have become the prevalent technology for high-performance energy storage systems. These are widely used as the main energy source for popular applications, including laptops, cell phones and other electronic devices. The typical LIB consists of two (negative and positive) electrodes, separated by an electrolyte. This plays a very important role, transferring ions between the electrodes, therefore providing the electrical current. This thesis work focuses on the complex materials used as electrolytes in LIBs, which impact Li-ion transport properties, power densities and electrochemical performances. Usually, the electrolyte consists of Li-salts and mixtures of organic solvents, such as cyclic or linear carbonates. It is therefore indispensable to shed light on the most important structural (coordination) properties, and their implications on transport behaviour of Li+ ion in pure and mixed solvent compositions. We have performed a theoretical investigation based on combined density Functional Theory (DFT) calculations and Molecular Dynamics (MD) simulations, and have focused on three carbonates, cyclic ethylene carbonate (EC) and propylene carbonate (PC), and linear dimethyl carbonate (DMC). DFT calculations have provided a detailed picture for the optimized structures of isolated carbonate molecules and Li+ ion, including pure clusters Li+(S)n (S=EC, PC, DMC and n=1-5), mixed binary clusters, Li+(S1)m(S2)n (S1, S2 =EC, PC, DMC, with m+n=4), and ternary clusters Li+(EC)l(DMC)m(PC)n with l+m+n=4. Pure solvent clusters were also studied including the effect of PF6- anion. We have investigated in details the structure of the coordination shell around Li+ for all cases. Our results show that clusters such as Li+(EC)4, Li+(DMC)4 and Li+(PC)3 are the most stable, according to Gibbs free energy values, in agreement with previous experimental and theoretical studies. The calculated Gibbs free energies of reactions in binary mixtures suggest that the addition of EC and PC molecules to the Li+-DMC clusters are more favourable than the addition of DMC to Li+-EC and Li+-PC clusters. In most of the cases, the substitution of solvent to binary mixtures are unfavourable. In the case of ternary mixtures, the DMC molecule cannot replace EC and PC, while PC can easily substitute both EC and DMC molecules. Our study shows that PC tends to substitute EC in the solvation shell. We have complemented our ab-initio studies by MD simulations of a Li-ion when immersed in the pure solvents and in particular solvents mixtures of interest for batteries applications, e.g. , EC:DMC (1:1) and EC:DMC:PC(1:1:3). MD is a very powerful tool and has allowed us to clarify the relevance of the cluster structures discovered by DFT when the ion is surrounded by bulk solvents. Indeed, DFT provides information about the most stable structures of isolated clusters but no information about their stability or multiplicity (entropy) when immersed in an infinite solvent environment. The MD data, together the DFT calculations have allowed us to give a very comprehensive picture of the local structure of solvent mixtures around Lithium ion, which substantially improve over previous work
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Liu, Xiao. "ATPG and DFT Algorithms for Delay Fault Testing." Diss., Virginia Tech, 2004. http://hdl.handle.net/10919/11213.
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With ever shrinking geometries, growing metal density and increasing clock rate on chips, delay testing is becoming a necessity in industry to maintain test quality for speed-related failures. The purpose of delay testing is to verify that the circuit operates correctly at the rated speed. However, functional tests for delay defects are usually unacceptable for large scale designs due to the prohibitive cost of functional test patterns and the difficulty in achieving very high fault coverage. Scan-based delay testing, which could ensure a high delay fault coverage at reasonable development cost, provides a good alternative to the at-speed functional test.
This dissertation addresses several key challenges in scan-based delay testing and develops efficient Automatic Test Pattern Generation (ATPG) and Design-for-testability (DFT) algorithms for delay testing. In the dissertation, two algorithms are first proposed for computing and applying transition test patterns using stuck-at test vectors, thus avoiding the need for a transition fault test generator. The experimental results show that we can improve both test data volume and test application time by 46.5% over a commercial transition ATPG tool. Secondly, we propose a hybrid scan-based delay testing technique for compact and high fault coverage test set, which combines the advantages of both the skewed-load and broadside test application methods. On an average, about 4.5% improvement in fault coverage is obtained by the hybrid approach over the broad-side approach, with very little hardware overhead. Thirdly, we propose and develop a constrained ATPG algorithm for scan-based delay testing, which addresses the overtesting problem due to the possible detection of functionally untestable faults in scan-based testing. The experimental results show that our method efficiently generates a test set for functionally testable transition faults and reduces the yield loss due to overtesting of functionally untestable transition faults. Finally, a new approach on identifying functionally untestable transition faults in non-scan sequential circuits is presented. We formulate a new dominance relationship for transition faults and use it to help identify more untestable transition faults on top of a fault-independent method based on static implications. The experimental results for ISCAS89 sequential benchmark circuits show that our approach can identify many more functionally untestable transition faults than previously reported.Ph. D.
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Rowson, Quinton Anthony. "Steady-state vibration of DFT locomotive cabs." Thesis, University of Canterbury. Mechanical Engineering, 2001. http://hdl.handle.net/10092/6624.
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Back injuries and other illnesses for Tranz Rails Locomotive Engineers, is claimed to be
attributed to vibration of locomotive cabs. The purpose of this research was to conduct a
study in order to determine the complex motion of a DFT locomotive cab and to
objectively and quantifiably measure the vibration present in the locomotive.
This thesis examines the ability of a six Degrees Of Freedom rigid body mathematical
model of a DFT locomotive cab to determine the natural frequencies present. The goal
was to use this model to provide information on different mount alternatives, in order to
reduce vibration. The results of this model were inadequate for the selection of another
elastomeric mounting alternative. While experimental test of the locomotive cab showed
that the rigid body assumption was valid it was found that there are other continuous
vibrations and non-linear effects that are also very important in determining cab
vibration.
Auto-correlation results from acceleration measurements at the base of the mounts were
overlaid with the cross-correlation of the acceleration measurements of the cab side of the
mounts. These results showed that the current mounts have 100% transmissibility. In
some cases and directions the mount was shown to actually amplify the vibrational input
from the locomotive.
The amplitude of the steady-state vibration of the locomotive cab that was being
transmitted was so great that it rendered the dynamic characteristics of the cab
insignificant. From the experimental results, the elastomeric mounts were found to be
incapable of attenuating the vibration. In addition, the vibration levels due to locomotive
running are found to be well above comfort levels of various publications.
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Knottenbelt, Sushilla. "A DFT study of metal-metal bonding." Thesis, University of York, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.424531.
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Reinhold, Meike. "A DFT study of organometallic reaction mechanisms." Thesis, University of York, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.247161.
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Pittock, Chris. "Using linear-scaling DFT for biomolecular simulations." Thesis, University of Southampton, 2014. https://eprints.soton.ac.uk/362968/.
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In the drug discovery process, there are multiple factors that make a successful candidate other than whether it antagonises a chosen active site, or performs allosteric regulation. Each test candidate is profiled by its absorption into the bloodstream, distribution throughout the organism, its products of metabolism, method of excretion, and overall toxicity; summarised as ADMET. There are currently methods to calculate and predict such properties, but the majority of these involve rule-based, empirical approaches that run the risk of lacking accuracy as one's search of chemical space ventures into the more novel. The lack of experimental data on organometallic systems also means that some of these methods refuse to predict properties on them outright, losing the opportunity to exploit this relatively untapped area that holds promise for new antibacterial and antineoplastic pharmaceutical compounds. Using the more transferable and definitive quantum mechanical (QM) approach to drug discovery is desirable, but the computational cost of conventional Hartree-Fock (HF) and Density Functional Theory (DFT) calculations are too high. Using the linear-scaling DFT program, onetep, we aim to exploit the benefits of DFT in calculations with much larger fragments of, and in some cases entire biomolecules, in order to demonstrate calculations which could ultimately be used in developing more accurate methods of profiling drug candidates, with a computational cost that albeit still high, is now feasible with the provision of modern supercomputers. In this thesis, we first use linear-scaling DFT methods to address the lack of electron polarisation and charge transfer effects in energy calculations using a molecular mechanics forcefield. Multiple DFT calculations are performed on molecular dynamics(MD) snapshots of small molecules in a waterbox, with the aim of computing a MM!QM correction term, which can be applied to a forcefield binding free energy approach (such as thermodynamic integration) which will process a far greater number of MD snapshots. As a result, one will obtain the precision from processing very large numbers of MD snapshots of biomolecular systems, but the accuracy of QM. To improve efficiency of the QM phase of the overall method, we use electrostatic embedding to model the regions of the waterbox that are far from the solute, yet are still important to include. As this is a relatively new module in onetep, we present validation data prior to its use in the main work. Secondly, we validate different methods of calculating the pKa of a wide variety of molecules: from small, organic compounds, to the organometallic cisplatin, with the ultimate goal being of such calculations to eventually address questions such as, assuming oral intake, where in the gastrointestinal tract will a drug molecule be absorbed into the bloodstream, and how much of the original dose will be absorbed. These calculations are then scaled up significantly to examine the potential of using linear-scaling DFT to calculate the pKa of specific residues in proteins. This is performed with a 305-atom tryptophan cage, the 814-atom Ovomucoid Silver Pheasant Third Domain(OMSVP3) and a 2346-atom section of the T99A/M102Q T4-lysozyme mutant. We also highlight the challenges in calculating protein pKa. Finally, we study the hydrogen-abstraction reaction between cyclohexene and cytochrome P450cam, through onetep single point energy calculations of a 10-snapshot adiabaticreaction profile generated by the Mulholland Group(University of Bristol). Following this, the LST and QST methods of determining the transition state (available through onetep) are used, with the aims of determining the importance of the protein surrounding the active site in regards to the activation energy and structural geometry of the calculated transition state. The LST and QST methods are also validated, through modelling of the SN2 reaction between fluoride and chloromethane. The aim of this part of our work is to eventually assist in developing a metabolism (and toxicity) model of the different isoforms of cytochrome P450. Overall, this thesis aims to highlight not only the capability of linear-scaling DFT in becoming an important part of biomolecular simulation, but also the challenges that one will face upon scaling up calculations that were previously simple to perform, based on the small size of the system being modelled.
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Buono, Carlo. "A DFT study of graphite supported catalysts." Thesis, Cardiff University, 2016. http://orca.cf.ac.uk/101043/.
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Gold catalysed hydrochlorination of acetylene is a convenient alternative to the use of toxic mercury derivatives in large scale production of vinyl chloride. The catalytic performance of supported gold nanoparticles is highly dependent on a series of factors. Amongst them the catalyst support plays a fundamental role. Acid wash of carbonaceous supports has proven to influence the catalytic performances of gold nanoparticles. Atomic force microscopy revealed that after acid treatments the morphology of the graphite support presents spherical features. X-ray photoemission spectra detected the presence of hydroxyl and carbonyl groups which were formed at the surface sites after acid treatments. DFT calculations have been used to give an insight on the mechanisms of formation these features, functional groups and, to support the experimental data. In good agreement with the experiment, it has been found that when water molecules are intercalated within the interlayer space, the graphitic surface presents a curvature and the interlayer distance is largely increased. While pristine graphite is hydrophobic and inert to water, defective surfaces presenting under coordinated carbons show increased reactivity and are able to dissociate water also at room temperature. Pristine graphite surface has a poor particle adhesion but unsaturated carbons of defects or edges can chemisorb atoms and molecules to form strong bonds. Finally, in good agreement with the experiment, DFT results show that the interactions between gold nanoparticles and the hydroxyl groups are stronger than those between gold and carboxyl groups suggesting that the hydroxyls are better anchoring sites for gold nanoparticles than carbonyls.
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Panta, Uday. "Charge Separation in Nano-diamonds: DFT Study." Bowling Green State University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1594381914885325.
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Grånäs, Oscar. "Theoretical Studies of Magnetism and Electron Correlation in Solids." Doctoral thesis, Uppsala universitet, Materialteori, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-172334.
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This work presents new development and applications of ab-initio simulation tools for material science. Focus lies on materials with strong electronic correlation and strong spin-orbit coupling. Improvements on methods for solving the impurity problem in LDA+DMFT is presented, as well as a reliant method for charge self-consistency in a LMTO based electronic structure code. A new adaptive scheme for Brillouin zone integration is developed, where we show a strong reduction of numerical noise compared to standard techniques. A reformulation of the standard LDA+U method aiming to reduce the number of free parameters is introduced. Fast and realistic reduction of the number of free parameters provides the possibility of high throughput calculations and enabled us to study a large number of compounds. An analysis method for polarization in terms of coupled multipoles, and their corresponding energy contributions is developed and applied. This led to the formulation of Katt's rules, a set of rules complementary to Hund's rules. Katt's rules applies for occupying the orbitals of an electronic shell with strong spin-orbit coupling. The analysis is also used to investigate the unconventional Uranium based superconductors URu2Si2, UPt3, UPd2Al3 and UNi2Al3, as well as the high temperature superconductor LaOFeAs. We also investigate the non-magnetic delta-phase of Plutonium, providing insight to the electronic structure and the branching ratios of 4d to 5f transitions seen in photo emission spectra.The influence of surface reconstruction on the magneto crystalline anisotropy is investigated in multilayer Fe/ZnSe, showing that Fe deposited on an unreconstructed interface strongly reduces the uniaxial component of the MAE. We provide a detailed understanding of the magnetic properties of Fe2P, opening possible routes for enhancing the MAE in this system. A general route to strong MAE in nano-laminates is presented, we apply this to propose a candidate with extremely strong anisotropy energy density, 5Fe/2W1-xReX for x=[0.6-0.8].
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Aguiar, Acrisio Lins de. "Estudo da interaÃÃo da Benzonitrila com Nanoestruturas de Carbono (Nanotubos, Grafeno e Fulereno)." Universidade Federal do CearÃ, 2008. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=1205.
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Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgicoNeste trabalho realizamos cÃlculos de primeiros princÃpios da interaÃÃo da benzonitrila (uma tÃpica base de Lewis) com vÃrias nanoestruturas de carbono: Nanotubos de Carbono de Parede Simples, Grafeno e Fulerenos. Utilizamos de algumas modificaÃÃes quÃmicas tais como dopagens e modificaÃÃes estruturais tais como a introduÃÃo de defeitos visando analisar possÃveis modificaÃÃes em nÃvel eletrÃnico nestas estruturas de carbono. Os cÃlculos ab initio sÃo baseados na teoria do funcional da densidade dentro das aproximaÃÃes da densidade local (LDA) e do gradiente da densidade para o termo de troca e correlaÃÃo. Os cÃlculos de energia total, com ou sem polarizaÃÃo de spin, foram realizados utilizando o cÃdigo SIESTA, o qual tÃm se mostrado bastante eficiente nos cÃlculos de primeiros princÃpios. Os cÃlculos mostraram que a benzonitrila interage fracamente com nanotubos de carbono puros. A interaÃÃo à relativamente mais forte via interaÃÃo entre os anÃis aromÃticos ($pi-pi$) do que via o grupo nitrila ($pi$-CN). Este comportamento à praticamente o mesmo quando modificamos os nanotubos de carbono atravÃs de um defeito (retirada de um Ãtomo de carbono) significando que os defeitos nÃo promovem a interaÃÃo com a benzonitrila. Os cÃlculos com grafeno mostraram uma interaÃÃo relativamente mais forte via interaÃÃo $pi-pi$ do que em nanotubos de carbono. CÃlculos com o fulereno C60 puro tambÃm mostraram que a interaÃÃo da benzonitrila à fraca com essas molÃculas. A interaÃÃo torna-se mais intensa no que diz respeito à transferÃncia de carga e grandes modificaÃÃes na estrutura eletrÃnica quando introduzimos um Ãtomo de Ferro nas paredes dos Nanotubos de Carbono e dos Fulerenos. As previsÃes teÃricas sÃo suportadas por experimentos espectroscÃpios realizados em amostram de nanotubos de carbono colocadas em contato com a benzonitrila comfirmando que a benzonitrila nÃo altera significativamente as propriedades dos nanotubos de carbono. Imagens de microscopia eletrÃnica revelam que a benzonitrila interage mais fortemente com partÃculas catalÃticas e com nanopartÃculas de carbono do que propriamente com Nanotubos de Carbono. Experimentos Ãticos (Infravermelho, Raman, AbsorÃÃo e EmissÃo) tambÃm revelam que a benzonitrila pouco interage com Nanotubos de Carbono purificados.
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Sousa, José Eduardo Padilha de. "Nanodispositivos baseados em grafeno." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-07082012-180729/.
Full textAbstract:
Nesta tese investigamos a partir de cálculos de primeiros princípios, dispositivos e componentes de dispositivos baseados em grafeno. Abordamos os campos da nanoeletrônica e da spintrônica. Dentro da nanoeletrônica investigamos: (i) propriedades de transporte de um nanotransistor de bicamada de grafeno na presença de um gate duplo. Demonstramos que sobre a ação de um campo elétrico externo, mesmo utilizando um gate da ordem de 10 nm, à temperatura ambiente e 4.5K uma corrente nula nunca é exibida. Esses resultados são explicados por um regime de tunelamento; (ii) propriedades eletrônicas e de transporte de multicamadas de grafeno em função do número de camadas e tipo de empilhamento entre elas. Mostramos que a estrutura eletrônica do sistema depende fortemente desse novo grau de liberdade de empilhamento. Na presença de um campo elétrico externo aplicado perpendicular ao sistema, o empilhamento do tipo Bernal nunca exibe um gap de energia, ao contrário do empilhamento romboédrico que exige um gap ajustável através da intensidade do campo. Mostramos também que é possível diferenciar os tipos de empilhamentos através da resistência do sistema e variando-se a temperatura; (iii) dentro das componentes de um nanotransistor mais realista, estudamos as propriedades eletrônicas e estruturais de: (a) bicamadas de grafeno sobre um substrato de nitreto de boro hexagonal. Neste sistema o limite de voltagens que podem ser aplicadas depende fortemente do número de camadas de h-BN e da direção do campo, onde quanto menos camadas maior é a voltagem que pode ser aplicada; (b) heteroestruturas compostas de bicamadas de grafeno, nitreto de boro hexagonal e cobre. Demonstramos que para uma aplicação direta em um dispositivo a configuração com uma bicamada de grafeno depositada sobre um substrato de h-BN e este conjunto sobre a superfície de cobre é a mais favorável. Nessa configuração é possível tanto controlar o gap na bicamada como a dopagem do sistema, sem a abertura de canais de condução através do dielétrico (h-BN). Dentro do campo da spintrônica estudamos: (i) propriedades de transporte das nanofitas de grafeno (GNR) (3,0) pristinas e dopadas com boro e nitrogênio. Para as GNR pristinas mostramos com os eletrodos em um alinhamento de spin anti-paralelo o sistema apresenta um comportamento de filtro de spin, onde para tensões de bias positivos/negativos somente o canal up/down conduz. Para as GNR dopadas com boro e nitrogênio, mostramos que as correntes para os diferentes canais de spin são não degeneradas ao longo de todo o intervalo de tensões aplicadas, apresentando desse modo um comportamento de filtro de spin; (ii) finalmente estudamos as propriedades de transporte de uma junção túnel magnética, composta de GNR intercaladas por uma nanofita de nitreto de boro hexagonal. Mostramos que esse sistema pode ser utilizado tanto como filtros de spin como elementos para dispositivos de magnetoresistência gigante, onde para este último a sua eficiência é muito mais pronunciada.In this thesis we investigated by first principle calculations, devices and components of devices based on graphene. We covered the fields of nanoelectronics and spintronics. On the field of nanoelectronics we investigated: (i) the transport properties of a dual gate bilayer graphene nanotransistor. We showed that under the action of an external electrical field, even with a gate length of 10 nm, at room temperature and 4.5K a zero current is never exhibited. These results could be explained by a tunneling regime; (ii) the electronic and transport properties of few layer graphene, as function of the number and type of stacking of the layers. We show that the electronic structure strong deppends of the stacking order. On the presence of a external electrical field applied to the system, the Bernal stacking never presents a gap, contrary to the rombohedrical one, that posses a tuneable energy gap. Also we showed that is possible to differentiate the types of stacking by the resistance of the system and varying the temperature;(iii) for the components of a more realistic nanodevice, we study the structural and electronic properties of: (a) bilayer graphene over a hexagonal boron nitride substrate. We show that the voltages that could be applied to the system strongly depends of the number 0 layers and the direction of the field, where with more layers, smaller is the field; (b) heterostructures composed with bilayer graphene, hexagonal boron nitride and cooper. We show that for a direct application on a device, the better configuration is with a bilayer graphene over the hexagonal boron nitride, and this set over a cooper. In this configuration is possible to control both the gap and the doping of the system, without the creation of conducting channels through the dielectric (h-BN). On the field of spintronics, we study: (i) the transport properties (3,0) graphene nanoribbons pristines and doped with nitrogen and boron. For the pristine GNR we show that for the electrodes in an anti-parallel alignment the system presents a spin filter behavior, where for positive/negative bias the transport is only by up/down channel. For the GNR doped with nitrogen and boron we show that the current is non-degenerated in all range of voltages applied, presenting a spin filter behavior; (ii) finally, we study the transport properties of a magnetic tunnel junction, consisting of a GNR intercalated with a hexagonal boron nitride nanoribbon. We show that such system could be used both as a spin filter as a device that uses the the giant magnetoresistance effect, where for the last the system if more efficient.