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1
Brincat, Nick. "Density functional theory investigation of the uranium oxides." Thesis, University of Bath, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.665418.
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The aim of this thesis is to provide insight into the structures and properties of the uranium oxides. As UO2 is easily oxidised during the nuclear fuel cycle it is important to have a detailed understanding of the structures and properties of the oxidation products. Experimental work over the years has revealed many stable oxides including UO2, U4O9, U3O7, U2O5, U3O8 and UO3, all with a number of different polymorphs. The oxides are broadly split into two categories, fluorite-based structures with stoichiometries in the range of UO2 to U2O5 and less dense layered-type structures with stoichiometries in the range of U2O5 to UO3. While UO2 is well characterised, both experimentally and computationally, there is a paucity of data concerning higher stoichiometry oxides in the literature. Experiments and simulations are emerging that deal with individual phases, however a comprehensive study that assesses the properties of all polymorphs and provides comparison over the full range of stoichiometries has been lacking from the literature First the nuclear fuel cycle is introduced, as well as UO2 as a nuclear fuel (Chapter 1), before the quantum mechanical methodology used throughout is explained (Chapter 2). Applying a number of different density functionals (including GGAs, meta-GGAs and hybrids) to UO2 in Chapter 3 it emerges that the PBE + U formalism reproduces the experimentally observed properties to a good degree of accuracy, and so is selected for the rest of the simulations. Following this Chapter 4 examines defect clusters in UO2, finding split interstitials to dominate at low stoichiometry (UO2 – UO2.0625), chains of 2:2:2 Willis clusters at higher stoichiometry (UO2.125 – UO2.25 (U4O9)) and split quad interstitials at higher stoichiometry (UO2.33 (U3O7)). Chapter 5 is an investigation of layered U2O5, where it emerges that the Np2O5 structure is more stable than δ-U2O5 and all uranium ions are in the U5+ oxidation state. Next Chapter 6 considers layered U3O8, which is structurally oxygen rich U2O5, where it is found that U5+ and U6+ ions exist in pentagonal bipyramidal and octahedral coordination respectively. The final set of results in Chapter 7 concern the polymorphs of UO3, where it is found that U6+ adopts a range of coordination environments and the predicted relative stability of each modification matches well with experiment. Finally the conclusions are presented in Chapter 8 along with plans for future work.
2
Zurek, Eva D. "Density functional theory (DFT) studies of solids and molecules." [S.l. : s.n.], 2006. http://nbn-resolving.de/urn:nbn:de:bsz:93-opus-27968.
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3
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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4
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.
5
Jirlén, Johan, and Emil Kauppi. "Carbon Nanotube Raman Spectra Calculations using Density Functional Theory." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-62169.
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Utilizing density functional theory (DFT) the Vienna Ab initio Simulation Package (VASP) was used to calculate the Raman spectra for five single-walled carbon nanotubes (SWCNTs) with chiralities (4,4), (6,6), (8,0), (12,0) and (7,1). The radial breathing mode (RBM), when compared with experimental frequencies, shows good correlation. When compared to RBM:s calculated with tight binding the frequencies calculated with DFT displayed higher accuracy. The precision of G-band frequencies were inconclusive due to lack of experimental data. The frequencies did not agree well with the results from tight-binding theory. The correctness of the Raman activity estimations using results from DFT calculations was found to be questionable. An unknown mode, which was found to be highly Raman active in the calculated spectra of (4,4), (6,6), and possibly (8,0), and (12,0), is also discussed. It was concluded that further calculations on larger tubes, especially armchair tubes are relevant for future studies. Further verification of the determination of Raman activity is also needed.Supervisors: Daniel Hedman, Andreas Larsson and Sven Öberg
F7042T - Project in Engineering Physics
6
Elgammal, Karim. "Density Functional Theory Calculations of Graphene based Humidity and Carbon Dioxide Sensors." Licentiate thesis, KTH, Materialfysik, MF, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-180761.
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Graphene has many interesting physical properties which makes it useful for plenty of applications. In this work we investigate the possibility of using graphene as a carbon dioxide and humidity sensor. Carbon dioxide and water adsorbates are modeled on top of the surface of a graphene sheet, which themselves lie on one of two types of silica substrates or sapphire substrate. We evaluate the changes in the electronic and structural properties of the graphene sheet in the presence of the described adsorbates as well as the accompanying substrate. We perform the study using ab-initio calculations based on density functional theory (DFT), that allows fast, accurate and efficient investigations. In particular, we focus our attention on investigating the effects of defects in the substrate and how it influences the properties of the graphene sheet. The defects of the substrate contribute with impurity bands leading to doping effects on the graphene sheet, which in turn together with the presence of the adsorbates result in changes of the electronic charge distribution in the system. We provide charge density difference plots to visualize these changes and also determine the relaxed minimum distances of the adsorbates from the graphene sheet together with the respective minimum energy configurations. We also include the density of states, Löwdin charges and work functions for further investigations.Grafen har många intressanta fysikaliska egenskaper, vilket gör det användbart för många tillämpningar. I detta arbete har vi teoretiskt undersökt möjligheten att använda grafen som gassensor för koldioxid och fukt. Adsorberade koldioxid- och vattenmolekyler modelleras ovanför ytan av ett lager grafen, som i sig ligger ovanpå en av två typer av kiseldioxidsubstrat eller ett aluminiumoxidsubstrat. Vi har utvärderat förändringar i de elektroniska och strukturella egenskaperna hos grafenlagret i närvaro av de beskrivna molekylerna samt åtföljande substrat. Vi utför studien med ab-initio beräkningar baserade på täthetsfunktionalteori (DFT), som möjliggör snabba, korrekta och effektiva elektronstruktursberäkningar. Framför allt fokuserar vi på effekten av defekter i underlaget, och hur dessa påverkar egenskaperna hos grafenlagret. Defekter i underlaget bidrar genom att införa elektroniska band som leder till dopningseffekter i grafenlagret, vilket i sin tur tillsammans med närvaron av adsorbatmolekylerna leder till förändringar av den elektroniska laddningsfördelningen i systemet. Vi tillhandahåller s.k. laddningsdensitet-skillnadsfigurer som visualiserar dessa förändringar. Vi har även beräknat jämviktsavståndet mellan adsorbatmolekylerna och grafenlagret tillsammans med respektive minimienergikonfigurationer för molekylerna, Vi åksa tillhandahåller täthet av stater, Löwdin laddningar och arbetsfunktion för fortsatta undersökningar.
QC 20160218
7
Beal, Nathan James. "Broken symmetry density functional theory studies of multinuclear manganese metalloproteins." Thesis, University of Manchester, 2017. https://www.research.manchester.ac.uk/portal/en/theses/broken-symmetry-density-functional-theory-studies-of-multinuclear-manganese-metalloproteins(37a587b1-0e91-4d9d-af74-95dd57573476).html.
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The photosynthetic water splitting reaction performed in green plants, algae and cyanobacteria is perhaps one of the most important reactions on the planet. The reaction is catalysed by a tetranuclear manganese cluster that is driven by sunlight and as such has received a high degree of interest in the context of solar fuels research. Due to the intricacy of the bioinorganic systems, the molecular mechanisms of the reactions are unknown and structural elucidation of the active sites is complicated. Computational techniques can provide considerable support in the analysis and interpretation of the complex EPR spectra of such biological systems. In this work, the molecular and electronic structures of several multinuclear manganese containing bioinorganic systems are investigated using BS-DFT. A particular focus of this work is the provision of high quality calculated EPR parameters yielding structural and mechanistic insight. In the first results chapter, the MnIIIMnIV superoxidised state of manganese catalase as well as azide inhibited manganese catalase is studied. Several variants are proposed and analysed on the basis of their calculated EPR parameters. The results presented in this chapter offer a new interpretation of previous experimental assignments. Chapter 6 features investigations on the S2 state of the Oxygen Evolving Complex of Photosystem II. In this chapter both the native OEC as well as the strontium substituted OEC are studied, in order to investigate how replacement of the calcium ion affects the structure of the OEC. The final results chapter presents calculations on the split signal S2Yz dot radical formed on the transition from the S2 to S3 state, as well as studying the S3 state. The calculation of various EPR hyperfine couplings and their comparison with available experimental data has provided key insights into the electronic structure of the OEC.
8
Dogaru, Daniela. "Hydrogenase Inhibition by O2: Density Functional Theory/Molecular Mechanics Investigation." Cleveland State University / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=csu1231721611.
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9
GRECO, CLAUDIO. "A DFT and QM/MM Investigation on Models Related to the [FeFe]-Hydrogenase Active Site." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2007. http://hdl.handle.net/10281/45775.
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In the present thesis, a theoretical investigation is described regarding hydroge-
nases - enzymes that are able to catalyze the reversible oxidation of molecular
hydrogen: H2
2H+ + 2e− . Such a very simple reaction could have fundamen-
tal importance for the possible future development of a hydrogen-based econ-
omy. However, the current approaches for molecular hydrogen oxidation imply
the use of very expensive platinum-containing catalysts, while H2 production at
industrial level still depends on hydrocarbons. In this framework, hydrogenases
represent a model for the development of new-generation catalysts, as they con-
tain only inexpensive transition metal cofactors (iron and/or nickel ions) and
are able to evolve hydrogen directly from acidic aqueous solutions supplied with
a convenient source of electrons.
The present work deals with the characterization of a specific class of hydro-
genases, termed [FeFe]-hydrogenases. These enzymes contain in their active site
a peculiar Fe6 S6 cluster - the so-called H-cluster - which can be ideally subdi-
vided in two distinct portions: a classical Fe4 S4 moiety, and a Fe2 S2 subcluster
(commonly termed [2Fe]H ) bearing CO and CN− ligands; these subclusters are
linked to each other through the sulphur atom of a cysteine residue. The two
iron atoms of the binuclear sub-site are termed proximal (Fep ) or distal (Fed ), de-
pending on their positions with respect to the Fe4 S4 moiety. Notably one of the
carbonyl groups included in the [2Fe]H subsite bridges the Fep and Fed centers,
and it moves to a semibridging position when the enzyme is in its completely
reduced form. The coordination environment of the iron ions included in the
binuclear cluster is completed by a bidentate ligand which has been proposed to
correspond either to a di(thiomethyl)amine (DTMA) or to a propanedithiolate
(PDT) residue.
Direct metal-hydrogen interaction at the binuclear sub-site is required for the
enzymatic activity of [FeFe]-hydrogenases; however, there is still some debate
about the way in which the interaction takes place, and about the catalytic
mechanism leading to H2 splitting/formation. In fact, despite the large number
of theoretical and experimental investigations carried out to clarify the catalytic
mechanism of [FeFe]-hydrogenases, a direct comparison between the two more
plausible routes for dihydrogen evolution/oxidation - i.e. a path involving the
formation of metal-bound terminal hydrides, as opposed to a route that implies
the presence of a hydride bridging Fep and Fed - was still lacking. Such study
has then been carried out in our laboratories, using computational models of
the H-cluster binuclear subsite in the context of a Density Functional Theory
(DFT) representation; this work is presented in Chapter 2. It turns out that H2 formation can take place according to reaction pathways that imply initial
protonation of the Fe(I)-Fe(I) form of [2Fe]H , leading to a formal Fe(II)-Fe(II)
hydride species, subsequent monoelectron reduction to an Fe(II)-Fe(I) species,
further protonation, and H2 release. A comparison of pathways involving either
the initial protonation of Fed or protonation of the Fep -Fed bond shows also
that the former pathway is characterized by smaller activation barriers, as well
as a downhill free-energy profile, suggesting that it could be the H2 production
pathway operative in the enzyme.
The next chapter in the present thesis is devoted to the characterization
of CO-mediated enzyme inhibition; indeed, the enzyme active site is able to
bind exogenous carbon monoxide, and such an interaction impairs the catalytic
process of H2 production/oxidation. Experimental and computational studies
have converged towards the assignment of a Fe(I)Fe(II) state to the CO-inhibited
binuclear sub-cluster, while there is still much debate about the disposition of
CO and CN− ligands around Fed in this form. Our analysis is carried out us-
ing a hybrid quantum mechanical/molecular mechanical (QM/MM) approach;
this means that an all-atom model of the enzyme is used for studying different
geometrical configurations of the active site. This allows us to show that the
protein environment surrounding the H-cluster plays a crucial role in influenc-
ing the mechanism of CO-inhibition; as a result, the CO-inhibited H-cluster is
expected to be characterized by a terminal CO ligand trans to the μ-CO group
on Fed .
A QM/MM approach is also used in order to unravel key issues regarding the
activation of the enzyme from its completely oxidized inactive state (Hox inact ,
an enzyme form in which the [2Fe]H subcluster attains the Fe(II)Fe(II) redox
state), and the influence of the protein environment on the structural and cat-
alytic properties of the H-cluster (see Chapter 4). Our results show that, in
Hox inact , a water molecule is bound to Fed . The computed QM/MM energy
values for water binding to the diferrous subsite are in fact over 17 kcal mol−1 ;
however, the affinity towards water decreases by one order of magnitude af-
ter a one-electron reduction of Hox inact , thus leading to release of coordinated
water from the H-cluster. The investigation of a catalytic cycle of the [FeFe]-
hydrogenase that implies formation of a terminal hydride ion and a DTMA
molecule acting as acid/base catalyst indicates that all steps have reasonable
reaction energies, and that the influence of the protein on the thermodynamic
profile of H2 production catalysis is not negligible; QM/MM results show that
the interactions between the Fe2 S2 subsite and the protein environment could
give place to structural rearrangements of the H-cluster functional for catalysis,
provided that the bidentate ligand that bridges the iron atoms in the binuclear subsite is actually a DTMA residue.
In the last two studies included in the present thesis (Chapter 5 and Chapter
6), DFT investigations are presented regarding the characterization of two syn-
thetic model complexes that represent structural and functional model of the
[2Fe]H cluster: Fe2 (S2 C3 H6 )(CO)6 and (S2 C3 H6 )[Fe2 (CO)5 P(NC4 H8 )3 ]. Both
of them are known to be able to catalyze proton reduction in an electrochemical
cell, but the details of the electrocatalytic mechanisms leading to H2 produc-
tion needed clarification. As for Fe2 (S2 C3 H6 )(CO)6 (a), it is showed that, in the
early stages of the catalytic cycle, a neutral μ-H adduct is formed; mono-electron
reduction and subsequent protonation can give rise to a diprotonated neutral
species (a-μH-SH), which is characterized by a μ-H group, a protonated sulfur
atom and a CO group bridging the two iron centers, in agreement with experi-
mental IR data indicating the formation of a long-lived μ-CO species. H2 release
from a-μH-SH and its less stable isomer a-H2 is kinetically unfavourable, while
the corresponding monoanionic compounds (a-μH-SH− and a-H2 − ) are more
reactive in terms of dihydrogen evolution, in agreement with experimental data.
As far as (S2 C3 H6 )[Fe2 (CO)5 P(NC4 H8 )3 ] (A) is concerned, experimental
results have suggested that the presence of the electron donor P(NC4 H8 )3 ligand
in A could favour the formation of a μ-CO species similar to that observed in the
enzymatic cluster. However, insight into the structural features of key catalytic
intermediates deriving from reduction and protonation of A was still lacking.
Thus, in Chapter 6 we present results obtained using Density Functional Theory
to evaluate structures, relative stabilities and spectroscopic properties of several
species relevant for the electrocatalytic H2 evolving process.
The results enable us to unravel the structure of the μ-CO complex ex-
perimentally detected after monoelectronic reduction of A. Moreover, we show
that the introduction of the large electron-donor ligand P(NC4 H8 )3 in the bio-
mimetic complex does not favour the stabilization of terminal-hydride adducts,
which are expected to be very reactive in terms of H2 production.
The comparison of our findings with previous theoretical and experimental
results obtained on similar model complexes suggests that the introduction of
an electron donor ligand as good as P(NC4 H8 )3 , but less sterically demanding,
could represent a better choice to facilitate the formation of μ-CO complexes
more closely resembling the structure of the enzymatic cluster.
10
Telyatnyk, Lyudmyla. "Magnetic Resonance Parameters of Radicals Studied by Density Functional Theory Methods." Licentiate thesis, KTH, Biotechnology, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-1727.
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The recent state of art in the magnetic resonance area putsforward the electron paramagnetic resonance, EPR, and nuclearmagnetic resonance, NMR, experiments on prominent positions forinvestigations of molecular and electronic structure. A mostdifficult aspect of such experiments is usually the properinterpretation of data obtained from high-resolution spectra,that, however, at the same time opens a great challenge forpure theoretical methods to interpret the spectral features.This thesis constitutes an effort in this respect, as itpresents and discusses calculations of EPR and NMR parametersof paramagnetic molecules. The calculations are based on newmethodology for determination of properties of paramagneticmolecules in the framework of the density functional theory,which has been developed in our laboratory.
Paramagnetic molecules are, in some sense, very special. Thepresence of unpaired electrons essentially modifies theirspectra. The experimental determination of the magneticresonance parameters of such molecules is, especially in theNMR case, quite complicated and requires special techniques ofspectral detection. The significant efforts put into suchexperiments are completely justi fied though by the importantroles of paramagnetic species playing in many areas, such as,for example, molecular magnets, active centers in biologicalsystems, and defects in inorganic conductive materials.
The first two papers of this thesis deal with thetheoretical determination of NMR parameters, such as thenuclear shielding tensors and the chemical shifts, inparamagnetic nitroxides that form core units in molecularmagnets. The developed methodology aimed to realize highaccuracy in the calculations in order to achieve successfulapplications for the mentioned systems. Theeffects of hydrogenbonding are also described in that context. Our theory forevaluation of nuclear shielding tensors in paramagneticmolecules is consistent up to the second order in the finestructure constant and considers orbital, fully isotropicdipolar, and isotropic contact contributions to the shieldingtensor.
The next three projects concern electron paramagneticresonance. The wellknown EPR parameters, such as the g-tensorsand the hyperfine coupling constants are explored. Calculationsof electronic g-tensors were carried out in the framework of aspin-restricted open-shell Kohn-Sham method combined with thelinear response theory recently developed in our laboratory.The spincontamination problem is then automatically avoided.The solvent effects, described by the polarizable continuummodel, are also considered. For calculations of the hyperfinecoupling constants a so-called restricted-unrestricted approachhas been developed in the context of density functional theory.Comparison of experimentally and theoretically determinedparameters shows that qualitative mutual agreement of the twosets of data can be easily achieved by employing the proposedformalisms.
11
Wang, Xuelin. "The performance of density functional theory with the correlation consistent basis sets." Thesis, University of North Texas, 2005. https://digital.library.unt.edu/ark:/67531/metadc4830/.
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Density functional theory has been used in combination with the correlation consistent and polarization consistent basis sets to investigate the structures and energetics for a series of first-row closed shell and several second-row molecules of potential importance in atmospheric chemistry. The impact of basis set choice upon molecular description has been examined, and irregular convergence of molecular properties with respect to increasing basis set size for several functionals and molecules has been observed. The possible reasons and solutions for this unexpected behavior including the effect of contraction and uncontraction, of the basis set diffuse sp basis functions, basis set superposition error (BSSE) and core-valence sets also have been examined.
12
Warschkow, Oliver. "A divide-and-conquer implementation of the discrete variational DFT method for large molecular and solid systems." Thesis, University of Southampton, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.284652.
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Wang, Jiaqi. "Transition Metal Catalyzed Oxidative Cleavage of C-O Bond." Thesis, University of North Texas, 2015. https://digital.library.unt.edu/ark:/67531/metadc801914/.
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The focus of this thesis is on C-O bonds activation by transition metal atoms. Lignin is a potential alternative energy resource, but currently is an underused biomass species because of its highly branched structure. To aid in better understanding this species, the oxidative cleavage of the Cβ-O bond in an archetypal arylglycerol β-aryl ether (β–O–4 Linkage) model compound of lignin with late 3d, 4d, and 5d metals was investigated. Methoxyethane was utilized as a model molecule to study the activation of the C-O bond. Binding enthalpies (ΔHb), enthalpy formations (ΔH) and activation enthalpies (ΔH‡) have been studied at 298K to learn the energetic properties in the C-O bond cleavage in methoxyethane. Density functional theory (DFT) has become a common choice for the transition metal containing systems. It is important to select suitable functionals for the target reactions, especially for systems with degeneracies that lead to static correlation effects. A set of 26 density functionals including eight GGA, six meta-GGA, six hybrid-GGA, and six hybrid-meta-GGA were applied in order to investigate the performance of different types of density functionals for transition metal catalyzed C-O bond cleavage. A CR-CCSD(T)/aug-cc-pVTZ was used to calibrate the performance of different density functionals.
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Fellah, Mehmet Ferdi. "A Density Functional Theory Study Of Catalytic Epoxidation Of Ethylene And Propylene." Phd thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/3/12611228/index.pdf.
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The reactions which give the products ethylene oxide, vinyl alcohol, vinyl aldehyde and vinyl radical for ethylene oxidation and the reactions which give propylene oxide, propanal, acetone and pi-allyl radical for propylene oxidation were investigated by using Density Functional Theory (DFT) method with B3LYP/LanL2DZ and 6-31g(d,p) basis sets in Gaussian&rsquo03 software. Silver and silver oxide were used as catalyst surface cluster models. Surface comparison was made for silver (111), (110) and (100) surfaces. Ethylene oxidation reaction was studied on these silver surfaces. Oxygen effect on ethylene oxide formation reaction was also investigated on silver (111) surface. Ethylene and propylene oxidation reactions were completed on both Ag13(111) and Ag14O9(001) surface clusters. VASP software which utilizes periodic plane wave basis sets was also used to compare trends of reactions for ethylene and propylene oxidations obtained by using Gaussian&rsquo
03 software. According to results, silver (110) surface is more active for ethylene oxide formation than (111) and (100) surfaces. Hill site of (110) surface is much more active than hollow site of (110) surface since oxygen atom weakly adsorbed on hill site. Ethyl aldehyde and vinyl alcohol can not be formed on Ag(111) surface because of those higher activation barriers while ethylene oxide can be formed on cluster. Activation barrier for ethylene oxide formation decreases with increasing oxygen coverage on Ag(111) surface. Ethylene oxametallocycle intermediate molecule was not formed on Ag2O(001) surface while it is formed on surface oxide structure on Ag(111). Ethyl aldehyde and vinyl alcohol are not formed on silver oxide (001) surface. For propylene oxidation, &
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-allyl formation path has the lowest activation barrier explaining why silver is not a good catalyst for the propylene oxide formation while it is a good catalyst for the ethylene oxide formation. This situation is valid for silver oxide. Propylene oxide selectivity increased in the gas phase oxidation. The qualitative relative energy trend obtained by VASP software is the similar with that of calculations obtained by using GAUSSIAN&rsquo
03 software.
15
Paulino, Neto Romain. "Développement et application de méthodes corrélées pour la description de systèmes moléculaires." Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066216/document.
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Ces travaux de thèse se sont concentrés sur le développement, l'implémentation et l'application de différents types de méthodes quantiques prenant la corrélation électronique en compte, dans le but de fournir des outils performants pour la description de systèmes moléculaires à l'état fondamental et excité. La méthode dite DMRG (Density Matrix Renormalization Group) a été étudiée et un logiciel correspondant a été développé en FORTRAN. Cette méthode permet de limiter le nombre d'états électroniques à prendre en compte, ce qui fait gagner du temps de calcul, tout en assurant une précision des résultats du même ordre que celle fournie par les toutes meilleures méthodes post-Hartree-Fock actuelles. Dans la deuxième partie de cette thèse, nous avons utilisé une autre méthode : la DFT (Density Functional Theory). Une étude théorique a été effectuée sur deux fonctionnelles à séparation de portée (HISS-A et -B) afin d'évaluer dans quelle mesure ces fonctionnelles, développées au départ pour l'étude des systèmes métalliques, pouvaient être appliquées à la description de l'état fondamental et excité de systèmes moléculaires hautement conjugués. Nous avons également utilisé la DFT afin de modéliser et rationaliser le comportement photo-physique d'un composé moléculaire présentant une émission dite " duale ". Nous avons pu ainsi caractériser le comportement complexe de la molécule à l'état excité et expliquer les résultats surprenants qui avaient été observés, en particulier au niveau des spectres d'émission UV et d'excitation de fluorescence. Le phénomène d'émission duale observé a ainsi pu être lié à la présence d'un degré de liberté conformationnel important de la moléculeIn the last few years, a lot of energy has been put forward in the area of quantum chemistry to develop new methods, or to improve existing methods, that are able to describe very precisely the electronic structure of molecular systems. In this manuscript, a precise overview of such a method (namely the Density Matrix Renormalization Group, DMRG method) is given. A software able to carry out DMRG calculations has indeed been developed from scratch in the laboratory during this thesis. This method can be seen as a post-Hartree-Fock method, in which only the electronic states that are relevant for the correct description of the molecule are kept. In this way, the computational cost remains acceptable, and the results are in line with those given by "exact" methods such as full-CI. Density Functional Theory (DFT) has also been investigated in this work. DFT and TD-DFT calculations have indeed also been carried out. The performances of two middle-range-separated functionals, namely HISS-A and HISS-B, to describe electronic transitions in conjugated molecules have been probed in a theory vs. theory study. Those functionals, which had been first developed for the study of metals, show to be adequate for the correct description of electronic excitations of chromophores and of push-pull molecules. Optical properties of a dual emittor have also been studied using TD-DFT. The dual emission of this molecule has been shown to stem from the presence of two distinct emissive states, respectively of Intramolecular Charge Transfer (ICT) and locally excited (LE) nature. TD-DFT has allowed us to link those two emissive states to two different conformations of the molecule
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Cheng, Lei. "FIRST-PRINCIPLES DENSITY FUNCTIONAL THEORY STUDIES OF REACTIVITIES OF HETEROGENEOUS CATALYSTS DETERMINED BY STRUCTURE AND SUBSTRATE." OpenSIUC, 2009. https://opensiuc.lib.siu.edu/dissertations/99.
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In this dissertation, density functional theory (DFT) calculations were used to investigate (1)NO2 adsorption on BaO in NOx Storage Reduction (NSR) catalyst affected by the morphology of BaO and the γ-Al2O3 support, (2) energy barrier of H2 dissociative adsorption over Mg clusters affected by its electronic structure, and (3) comparison of the activities of CeO2 clusters affected by two different supports--monoclinic ZrO2 and non-spinel γ-Al2O3. Our results showed that the electronic effect caused by the non-stoichiometry of the bare BaO clusters and surfaces improves their reactivities toward NO2 adsorption greatly, whereas the geometric structure of the catalyst has only minor effect on the activity; we also found that the γ-Al2O3 substrate improves the reactivities of the supported BaO clusters and at the same time the interface between BaO and γ-Al2O3 provided a unique and highly reactive environment for NO2 adsorption. Hydrogen dissociation barrier over pure Mg clusters is greatly affected by the electronic structure of the clusters--closed shell clusters such as Mg10 and Mg92- have higher energy barrier toward H2 dissociation; however, H2 dissociation over clusters that are two electrons shy from the closed electronic shell are relatively easier. As substrates, neither ZrO2(111) nor γ-Al2O3(100) affects the reactivity of the supported Ce2O4 toward CO2 adsorption and CO physisorption significantly; whereas the reactivity of Ce2O4 toward CO reactive adsorption were found to be affected by the two substrates very differently.
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Moore, Corell H. "Modeling the peak absorption of MEH-PPV in various solvents using Density Functional Theory." VCU Scholars Compass, 2019. https://scholarscompass.vcu.edu/etd/6041.
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Density Functional Theory (DFT) and time-dependent Density Functional Theory (TD-DFT) are powerful tools for modeling orbital energy in conjugated molecules and have been useful tools for research in organic photovoltaics. In this work, DFT is first used to explain the red shift in the absorption spectrum and increased absorption observed in MEH-PPV. Initially, the modeling of the red-shift in the absorption peak of MEH-PPV is studied using Gaussian 03 software with the global hybrid functional B3LYP for exchange-correlation and the 6-31G basis set. DFT and TD-DFT are used to separately study the effects of polymer chain length, carbon-carbon double-bond stretching, and the polymer in solution vs. in gas space on red shift in absorption spectrum.
Next, Gaussian 09 software and the same B3LYP functional and 6-31G basis set are used to study interchain and intrachain interactions of MEH-PPV in solution. The red shift in the absorption peaks for three MEH-PPV configurations (single-chain pentamer, two stacked pentamers, and decamer) are compared with experimental results for five different solvents (chloroform, toluene, xylene, dichloromethane, and chlorobenzene). This investigation indicates that inter-chain interactions dominate in “good” aromatic solvents as compared to “poor” non-aromatic solvents. The results suggest that inter-chain charge transfer interactions play a critical role in real solutions and inter-chain aggregation takes precedence over intra-chain aggregation in aromatic solvents.
In the final section of the study, accurate values for the range-separation parameter (w) for three lengths of MEH-PPV polymer (trimer, tetramer, and pentamer) in five different solvents (chloroform, chlorobenzene, xylene, Tetrahydrofuran, and dichloromethane) are reported using the range-separated functionals wB97XD and CAM-B3LYP. Using these data, range separation parameters are predicted and used for longer polymer chains in chloroform solution. The differences in the range separation parameters for the different solvents is statistically significant and gives further insight into the polymer/solvent interaction.
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Ramachandran, Arathi. "Assessment of the accuracy of DFT (Density Functional Theory) for the photochromic behavior of dihydroazulene (DHA)." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/76126.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 39-42).
Efficient utilization of the sun as a renewable and clean energy source is one of the greatest goals and challenges of this century due to the increasing demand for energy and its environmental impact. Photoactive molecules that can store the sun's energy in the form of chemical bonds have been of interest to harness the sun's energy since the 1970s. However, all of the photoactive systems studied have problems with degradation making them impractical. Recently, the Grossman Group used computation to show that nanotemplating of the azobenzene photoactivesystem improves problems with degradation. We believe that this could be a platform technology for other photoactive systems like azobenzene. We would like to use high throughput screenings to identify other promising photoactive molecules. We would like to use Density Functional Theory (DFT) calculations for these studies, since DFT is the least computationally intense Quantum Mechanical model used on large chemical systems. For photosystems like azobenzene, nombomadiene, and diruthenium fulvalene, DFT predictions have been found to match well with experimental predictions, suggesting that DFT can be used to confidently predict properties of these fuels. However, for dihydroazulene(DHA) photoactive predictions using different DFT functionals do not match with each other and experiment. Our analysis suggests that lack of error cancelation due to a drastic change in the conjugation in DHA as compared to VHF might account for the variation in predictions based on different DFT functionals. It was also found that the DFT functional, [psi]B97X-D, makes similar predictions as the more computationally intense post Hartree-Fock methods by including couple cluster terms that better capture weak interactions.
by Arathi Ramachandran.
S.B.
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Mishra, D. "Structural, conformational and reactivity studies on DNA base pairs and phospholipids using density functional theory (DFT)." Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 2014. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/1937.
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Molfetta, Fabio Alberto de. "\"Planejamento de quinonas com atividade tripanossomicida\"." Universidade de São Paulo, 2007. http://www.teses.usp.br/teses/disponiveis/75/75131/tde-14052007-150816/.
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Desde a identificação do vírus da imunodeficiência humana (HIV, do inglês Human Immunodeficiency Virus) como agente causador da Síndrome da Imunodeficiência Adquirida (AIDS ? do inglês Acquired Immunodeficiency Syndrome), a busca para tratamentos seguros e eficazes contra o HIV transformou-se no principal foco para a descoberta de uma nova droga em todo o mundo. A AIDS aparece como um dos principais problemas de saúde pública para as próximas décadas, onde será o maior determinante de mortalidade na faixa etária entre 20 e 50 anos em praticamente todos os países do mundo. Tendo como objetivo relacionar a atividade de compostos biflavonóides anti-HIV-1 com algumas de suas propriedades moleculares, serão utilizados métodos de Mecânica Molecular e Química Quântica. O método de cálculo semi-empírico AM1 foi empregado para calcular um conjunto de propriedades moleculares dos 14 compostos biflavonóides com atividade anti-HIV-1. A seguir utilizar-se-á métodos estatísticos com a finalidade de separar os 14 compostos em duas classes, ativos e não ativos, de forma que se relacione qual as propriedades, dentre as calculadas, são responsáveis pela atividade dos compostos biflavonóides estudados. As técnicas estatísticas utilizadas foram a Análise de Componentes Principais (PCA: Principal Components Analysis), Análise Hierárquica de Agrupamentos (HCA: Hierarquical Clusters Analysis) e Análise de Discriminates por Passos (SDA: Stepwise Discriminant Analysis). Os estudos com PCA, HCA, e SDA mostraram que as variáveis HOMO (Highest Occupied Molecular Orbital - Orbital Molecular Ocupado de Maior Energia), LUMO (Lowest Unoccupied Molecular Orbital ? Orbital Molecular Desocupado de Menor Energia), e Área superficial são responsáveis pela separação dos compostos com alta e baixa atividade anti-HIV-1. O comportamento destas três propriedades pode ser útil na tentativa de se obter outros compostos biflavonóides com elevada atividade inibidora anti-HIV-1.A set of 25 quinone compounds with anti-trypanocidal activity was studied by using the Density Functional Theory (DFT) method in order to calculate electronic atomic and molecular properties to be correlated with the biological activity. The chemometric methods Principal Component Analysis (PCA), Hierarchical Cluster Analysis (HCA), Stepwise Discriminant Analysis (SDA), Kth nearest neighbor (KNN) and Soft Independent Modeling of Class Analogy (SIMCA) were used to obtain possible relationships between the calculated descriptors and the biological activity studied and predict the anti-trypanocidal activity of new quinone compounds from a test set. Four descriptors were responsible for the separation between the active and inactive compounds: T5 (torsion angle), HOMO-1 (energy of the first molecular orbital below HOMO), QTS1 (sum of absolute values of the atomic charges) and VOLS2 (volume of the substituent at region B). These descriptors give information on the kind of interaction that occurs between the compounds and the biological receptor. The prediction study was done with a set of three new quinone compounds by using the PCA, HCA, SDA, KNN and SIMCA. Beside the five chemometric methods, the neural network method was used by employing the backpropagation algorithm. The four variables (T5, QTS1, VOLS2 and HOMO-1) were employed to validate the models constructed previously. The architecture of networks consisting of four neurons at input layers, ten neurons at intermediary layers and two neurons at output layers was adopted to observe the root mean square error between the true and desired output over the entire training set. The percentage of correct classification was 87.5%, and only one compound was predicted wrong in the test set, which indicates that the model is robust and could be able to make predictions. The docking studies were carried out with two different programs in the approach of ligands: the Autodock and FlexX. The docking results on trypanothione reductase enzyme showed that all studied compounds stay at second hydrophobic pocket in the outer region of the active site called the Z-site. The residues that could be specifically involved in the binding of ligands are Lys62, Thr66, Thr397, Thr463, Leu399, Ser464, Glu466 and Glu467, where the residues Thr66, Thr463 and Leu399 are conserved in different trypanothiones and could be used for the development of selective inhibitors against to the parasite enzyme.
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Courtois, Julien. "Iridium-based bimetallic alloy catalysts for the ethanol oxidation reaction for fuel cells modeled by density functional theory." Digital WPI, 2013. https://digitalcommons.wpi.edu/etd-theses/295.
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Current ethanol oxidation catalysts in direct ethanol fuel cells (typically platinum-based) suffer from low conversion and are susceptible to CO poisoning. Therefore we determined to find viable alternative catalysts for ethanol oxidation based on iridium using density functional theory to model bimetallic alloy (111) surfaces. Iridium was alloyed with another transition metals M in an overlayer (one layer of metal M on top of bulk iridium) or subsurface configuration (M is inserted under the first layer of iridium). Complete oxidation of ethanol is limited by the breaking of strong C-C bonds, so any catalyst must lower the barriers for C-C bond breaking. We modeled the reaction CH+CO →CHCO.Segregation energies were calculated and the subsurface configuration was the most stable configuration in the vast majority of alloy cases. CO adsorption was also studied and a lower CO adsorption energy was found in many alloy cases compared to pure Pt (, providing encouraging results about the possibility of reducing CO poisoning. Activation energies were lowered for the vast majority of the alloys used in an underlayer structure, reinforcing our interest in the underlayer structures or “subsurfaceâ€� alloys. Finally, we found, based on the CO adsorption energies, activation energies of the C-C breakage reaction, and metal cost, three important catalyst descriptors, a number of promising catalysts for the ethanol oxidation reaction. The most interesting alloys all adopted the underlayer structure Ir/M/Ir. With M = Ta, Hf, Nb, V, Zr, they demonstrated enhanced reactivity and high CO tolerance, having the advantage of reducing the cost of the catalyst, potentially substituting expensive platinum group metals by more affordable components.
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Okhrimenko, Ivan Grigoryevich. "Implementation of Optical Spectra Calculations in FIREBALL: A Local-Orbital Density Functional Theory Approach." Diss., CLICK HERE for online access, 2008. http://contentdm.lib.byu.edu/ETD/image/etd2620.pdf.
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Kirgan, Robert A. "Diimine complexes of ruthenium(ii), rhenium(i) and iron(ii): from synthesis to DFT studies." Diss., Wichita State University, 2007. http://hdl.handle.net/10057/3981.
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The chloro and pyridinate derivatives of rhenium(I) tricarbonyl complexes containing the diimine ligands 2,2’-bipyrazine (bpz) and 5,5’-dimethyl-2,2’-bipyrazine (Me2bpz) are discussed. When compared to similar rhenium(I) tricarbonyl complexes of 2,2’-bipyridine (bpy) and 2,2’-bipyrimidine (bpm), the Me2bpz complexes are comparable to bpm derivatives and their properties are intermediate between those of bpy and bpz complexes.
Also discussed is the synthesis and properties of two new analogues of ruthenium(II) tris-bipyridine, a monomer and dimer. The complexes contain the ligand 6,6’-(1,2-ethanediyl)bis-2,2’-bipyridine (O-bpy) which contains two bipyridine units bridged in the 6,6’ positions by an ethylene group. Crystal structures of the two complexes formulated as [Ru(bpy)(O-bpy)](PF6)2 and [(Ru(bpy)2)2(O-bpy)](PF6)4 reveal structures of lower symmetry than D3 which affects the electronic properties of the complexes as revealed by Density Functional Theory (DFT) and Time Dependent Density Functional Theory (TDDFT) calculations. Iron(II) tris-bipyrazine undergoes dissociation in solution with loss of the three bipyrazine ligands. The rate of the reaction in acetonitrile depends on the concentration of anions present in the solution. The rate is fastest in the presence of Cl- and slowest in the presence of Br-. In a second discussion DFT calculations are used to explore four iron(II) diimine complexes. DFT calculations show the higher energy HOMO (highest occupied molecular orbital) orbitals of the four complexes are metal centered and the lower energy LUMO (lowest unoccupied molecular orbitals) are ligand centered.Dissertation(Ph.D.)--Wichita State University, College of Liberal Arts and Sciences, Dept. of Chemistry
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Ullah, Habib. "First-principles density functional theory study of novel materials for solar energy conversion and environment applications." Thesis, University of Exeter, 2018. http://hdl.handle.net/10871/32949.
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To design an efficient solar energy conversion device, theoretical input is extremely important to provide the basic guideline for experimental scientists, to fabricate the most efficient, cheap, and stable device with less efforts. This desire can be made possible if computational scientist use a proper theoretical protocol, design an energy material, then the experimentalist will only invest weeks or months on the synthetic effort. This thesis highlights my recent efforts in this direction. Monoclinic BiVO4 is has been using as a photocatalyst due to its stability, cheap, easily synthesizable, narrow band gap and ideal VB (-6.80 eV vs vacuum) but inappropriate CB (-4.56 eV vs vacuum) edge position, responsible for its low efficiency. We have carried out a comprehensive experimental and periodic density functional theory (DFT) simulations of the pristine, Oxygen defective (Ov), Se doped monoclinic BiVO4 and heterojunction with Selenium (Se-BiVO4), to improve not only its CB edge position but photocatalytic and charge carrier properties. It is found that Ov (1% Oxygen vacancy) and mild doped BiVO4 (1 to 2% Se) are thermodynamically stable, have ideal band edges ~ -4.30 eV), band gaps (~1.96 eV), and small effective masses of electrons and holes. We have also investigated the contribution of Se to higher performance by effecting morphology, light absorption and charge transfer properties in heterojunction. Finally, it is found that Se makes a direct Z-scheme (band alignments) with BiVO4 where the photoexcited electron of BiVO4 recombine with the VB of Se, consequences electron-hole separation at Se and BiVO4, respectively, as a result, enhanced photocurrent is obtained. Theoretical study of β-TaON in the form of primitive unit cell, supercell and its N, Ta, and O terminated surfaces are carried out with the help of periodic DFT. Optical and electronic properties of all these different species are simulated, which predict TaON as the best candidate for photocatalytic water splitting contrast to their Ta2O5 and Ta3N5 counterparts. The calculated bandgap, valence band, and conduction band edge positions predict that β-TaON should be an efficient photoanodic material. The valence band is made up of N 2p orbitals with a minor contribution from O 2p, while the conduction band is made up of Ta 5d. Turning to thin films, the valence band maximum; VBM (−6.4 eV vs. vacuum) and the conduction band minimum; CBM (−3.3 eV vs. vacuum) of (010)-O terminated surface are respectively well below and above the redox potentials of water as required for photocatalysis. Charge carriers have smaller effective masses than in the (001)-N terminated film (VBM −5.8 and CBM −3.7 eV vs. vacuum). However, due to wide band gap (3.0 eV) of (010)-O terminated surface, it cannot absorb visible wavelengths. On the other hand, the (001)-N terminated TaON thin film has a smaller band gap in the visible region (2.1 eV) but the bands are not aligned to the redox potential of water. Possibly a mixed phase material would produce an efficient photoanode for solar water splitting, where one phase performs the oxidation and the other reduction. Computational study of an optically transparent, near-infrared-absorbing low energy gap conjugated polymer, donor−acceptor−donor (D-A-D) with promising attributes for photovoltaic application is reported herein. The D and A moiety on the polymeric backbone have been found to be responsible for tuning the band gap, optical gap, open circuit (Voc) and short-circuit current density (Jsc) in the polymers solar cells (PSC). Reduction in the band gap, high charge transformation, and enhanced visible light absorption in the D-A-D system is because of strong overlapping of molecular orbitals of D and A. In addition, the enhanced planarity and weak steric hindrance between adjacent units of D-A-D, resulted in red-shifting of its onset of absorption. Finally, PSC properties of the designed D-A-D was modeled in the bulk heterojunction solar cell, which gives theoretical Voc of about 1.02 eV. DFT study has been carried out to design a new All-Solid-State dye-sensitized solar cell (SDSC), by applying a donor-acceptor conjugated polymer instead of liquid electrolyte. The typical redox mediator (I1−/I3−) is replaced with a narrow band gap, hole transporting material (HTM). A unique “upstairs” like band energy diagram is created by packing N3 between HTM and TiO2. Our theoretical simulations prove that the proposed configuration will be highly efficient as the HOMO level of HTM is 1.19 eV above the HOMO of sanitizer (dye); providing an efficient pathway for charge transfer. High short-circuit current density and power conversion efficiency is promised from the strong overlapping of molecular orbitals of HTM and sensitizer. A low reorganization energy of 0.21 eV and exciton binding energy of 0.55 eV, confirm the high efficiency of HTM. Theoretical and experimental studies of a series of four porphyrin-furan dyads were designed and synthesized, having anchoring groups, either at meso-phenyl or pyrrole-β position of a zinc porphyrin based on donor–π–acceptor (D–π–A) approach. The porphyrin macrocycle acts as donor, furan hetero cycle acts as π-spacer and either cyanoacetic acid or malonic acid group acts as acceptor. Optical bandgap, natural bonding, and molecular bonding orbital (HOMO–LUMO) analysis confirm the high efficiency pyrrole-β substituted zinc porphyrins contrast to meso-phenyl dyads. DFT study of polypyrrole-TiO2 composites has been carried out to explore their optical, electronic and charge transfer properties for the development of an efficient photocatalyst. Titanium dioxide (Ti16O32) was interacted with a range of pyrrole (Py) oligomers to predict the optimum composition of nPy-TiO2 composite with suitable band structure for efficient photocatalytic properties. The study has revealed that Py-Ti16O32 composites have narrow band gap and better visible light absorption capability compared to individual constituents. A red-shifting in λmax, narrowing band gap, and strong intermolecular interaction energy (-41 to −72 kcal/mol) of nPy-Ti16O32 composites confirm the existence of strong covalent type interactions. Electron−hole transferring phenomena are simulated with natural bonding orbital analysis where Py oligomers found as donor and Ti16O32 as an acceptor in nPy-Ti16O32 composites. Sensitivity and selectivity of polypyrrole (PPy) towards NH3, CO2 and CO have been studied at DFT. PPy oligomers are used both, in the doped (PPy+) and neutral (PPy) form, for their sensing abilities to realize the best state for gas sensing. Interaction energies and amount of charges (NBO and Mulliken charge analysis) are simulated which reveal the sensing ability of PPy towards these gases. PPy, both in doped and neutral state, is more sensitive to NH3 compared to CO2 and CO. More interestingly, NH3 causes doping of PPy and de-doping of PPy+, providing evidence that PPy/PPy+ is an excellent sensor for NH3 gas. UV-vis and UV-vis-near-IR spectra of nPy, nPy+, and nPy/nPy+-X complexes demonstrate strong interaction of PPy/PPy+ with these atmospheric gases. The applications of graphene (GR) and its derivatives in the field of composite materials for solar energy conversion, energy storage, environment purification and biosensor applications have been reviewed. The vast coverage of advancements in environmental applications of GR-based materials for photocatalytic degradation of organic pollutants, gas sensing and removal of heavy metal ions is presented. Additionally, the presences of graphene composites in the bio-sensing field have been also discussed in this review.
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Artuc, Zuleyha. "Density Functional Theory Investigation Of Noble Metal Reduction Agents On Gamma-al2o3 In Nox Storage/reduction Catalysis." Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613756/index.pdf.
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Pollution from automobile exhaust is one of the most major environmental problems because of increasing usage of engine technologies. Diesel and lean burn gasoline engines operate
under oxygen rich (lean) conditions and they emit harmfull gases to the atmosphere (CO,CO2, NO, NO2). The control of NOx emission from exhaust has become a challenging issue
in engine industry because of the worldwide environmental regulations. Therefore lean-burn NOx emission control technologies have been developed to reduce emission of harmfull gases from exhausts, and the NOx storage/reduction (NSR) catalysts is one of the most promising candidates to reduce the pollution caused by lean-burn engines. In NSR systems, NO from the emission is first oxidized to NO2 over noble metal sites (Pt, Rh, Pd) during lean-burn engine operation. After that NO2 is stored as nitrites and nitrates in alkali earth oxides (BaO,MgO, CaO) particles or monolayer which is well dispersed on a substrate (Gamma-Al2O3, TiO2,
SiO2). Finally, stored NOx compound are broken into N2 and O2 on noble metal sites. The Pt/BaO/Gamma-Al2O3 system is one of the most popular subjects in literature both experimentally and theoretically since this system is known to be catalytically more active and ecient in interactions between NOx and Pt-BaO components are still not clearly explained. For this reason, in this thesis, the interaction between catalytic redox components, Pt and Rh, and the support material
Gamma-Al2O3 and the eects of Pt and Rh in atomic and diatomic clusters forms on the adsorption of the NO2 molecule on the Gamma-Al2O3(100) surface have been investigated
by using density functional theory (DFT).
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Cavallucci, Tommaso. "Atomic and electronic properties of graphene based systems grown on silicon carbide: a density functional theory study." Doctoral thesis, Scuola Normale Superiore, 2018. http://hdl.handle.net/11384/85918.
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Alhabradi, Thuraya Faleh. "DFT Study of the Covalent Functionalization of Double Nitrogen Doped Graphene." DigitalCommons@Robert W. Woodruff Library, Atlanta University Center, 2018. http://digitalcommons.auctr.edu/cauetds/120.
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Covalent functionalization significantly enhances the utility of carbon nanomaterials for many applications. In this study, we investigated the functionalization of double nitrogen doped graphene by the addition of different alkyl and phenyl functional groups at N atoms in syn and anti-configurations. Density functional theory calculations at the B3LYP/def-SV(P) level were employed to understand the syn versus anti preference on functionalization. The bond lengths, bond angles, relative energies, deformation energies and HOMO-LUMO energy gaps, of the syn and anti-configurations of the functionalized 2N-doped graphenes, have been compared. Functionalization with two groups leads to considerable deformation of 2N-doped graphene, which is confirmed by the change in C–N bond lengths by attachment of the functional groups. The attachment of larger functional groups deforms 2N-doped graphene to a greater extent than smaller functional groups. The HOMO-LUMO energy gap values are the least for the alkyl functionalized products, indicating that these structures are kinetically less stable than the phenyl functionalized products.
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Weerasinghe, Krishanthi Chandima. "DENSITY FUNCTIONAL THEORY STUDIES OF PHOTOINDUCED ELECTRON EXCITATION AND TRANSFER OF ORGANIC DYES FOR PHOTODYNAMIC THERAPY, SOLAR CELLS, AND FLUORESCENCE SENSOR APPLICATIONS." OpenSIUC, 2016. https://opensiuc.lib.siu.edu/dissertations/1234.
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The main aim of work presented here is to understand photophysical processes of organic dyes and to design better organic molecules/systems which can be applied in many applications such as solar cells, photodynamic therapy, and fluorescence sensors. Developments of novel multichromophore organic materials for the above mentioned applications were made using computational tools. A brief description of the history of computational chemistry was given based on the photochemistry of organic dyes in the introductory chapters and also the importance of basis sets and functionals was discussed in order to produce accurate computational results. Density functional theory (DFT) and time-dependent DFT (TDDFT) calculations were performed to understand the photophysical processes in the porphyrin-perylene bisimide (HTPP-PDI) dyad that exhibited long-lived triplet states. The DFT results show that breaking the rigidity of PDI in HTPP-PDI was responsible for the generation of long-lived triplet states. Furthermore, six porphyrin derivatives were designed by introducing a 4,4’-dicarboxybutadienyl functional group to the porphyrin moiety and studied to investigate the substituent effects on the non-coplanarity, molecular orbitals, and excitation wavelength of the porphyrin donor. Five of the six proposed porphyrin derivatives are promising donors in the HTPP-PDI dyad to replace HTPP for its potential use in photodynamic therapy. Six donor- accepter(s) systems were designed for their potential application in solar cells. Four D-A1-A2 architectural triads, MTPA-TRC-AEAQ, MTPA-TRC-HTPP, MTPA-TRC-PDI, and MTPA-TRC-PBI were designed. The cascade electronic energy levels were obtained and experimentally observed, which lead to sequential electron transfers from 1MTPA* to TRC and then to AEAQ (HTPP/PDI/PBI) module as well as a hole transfer from 1AEAQ*(1HTPP*/1PDI*/1PBI*) to MTPA module. Therefore, all the D-A1-A2 systems we have designed are ambipolar. Interestingly, the lifetime of charge separated states of the newly designed MTPA*+-TRC-AEAQ*- was elongated to 650 ns, an eightfold of that of the donor-acceptor MTPA-TRC parent molecule (80 ns). However, different charge separated state lifetimes were obtained for MTPA*+-TRC-PDI*-(22ns) and MTPA*+-TRC-PBI*-(75ns). The photophysical results suggested that the charge separated state may decay to the triplet state when the charge separated state exhibits a higher energy level than the triplet state. Further, the photovoltaic tests indicated potential applications of MTPA-TRC-AEAQ in solar cells. DFT and TDDFT calculations were performed together with experimental studies to explore the nature of fluorescence enhancement in the anthracene-based sensor after the addition of Zn2+. A 23-fold fluorescence emission was quenched via non-radiative decay pathway in the absence of Zn2+. However, when the Zn2+ chelated to the sensor fluorescence intensity was increased remarkably. A 32-fold fluorescence increase was overserved and calculation results suggested this could be due to the inhibition of the electron-transfer pathway and enhanced rigidity of sensor-Zn2+ complex. The response selectivity of Zn2+ over Ca2+, Mg2+, Cu2+, and Hg2+ ions was also studied using DFT calculations and it was found that Zn2+ has a strong binding affinity to the sensor, which could be a potential application in the detection of Zn2+.
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Kuriakose, N. "Density functional theory (DFT) studies of the homogeneous activation of small molecules using transition metal and main group based compounds." Thesis(Ph.D.), CSIR-National Chemical Laboratory, Pune, 2015. http://dspace.ncl.res.in:8080/xmlui/handle/20.500.12252/2021.
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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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Kosak, Rukan. "The Effects Of Promoters On The Sulfur Resistance Of Nox Storage/reduction Catalysts: A Density Functional Theory Investigation." Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613442/index.pdf.
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High fossil fuel consumption in transportation and industry results in an increase of the emission of green-house gases. To preserve clean air, new strategies are required. The main intention is to decrease the amount of CO2 emission by using lean-burn engines while increasing the combustion efficiency and decreasing the fuel consumption. However, the lean-burn engines have high air-to-fuel ratio which complicates the reduction of the oxides of nitrogen, NOx . The emission of these highly noxious pollutants, NOx , breeds both environmental and health problems. Thus, new catalytic strategies have been steadily developed. One of these strategies is the NOx storage and reduction (NSR) catalysts. Since the reduction of the NOx under excess oxygen condition is very difficult, the NSR catalysts store the NOx until the end of the lean phase that is subsequently alternated with the rich-fuel phase during which the trapped NOx is released and reduced.
To develop NSR technology, different storage materials, the coverage of these metals/metal-oxides, support materials, precious metals, temperature, etc. have been widely investigated. In this thesis, the (100) surface of BaO with dopants (K, Na, Ca and La), (100) and (110) surfaces of Li2O, Na2O and K2O are investigated as storage materials. In addition, alkali metal (Li, Na and K) loaded (001) surface of TiO2 (titania) anatase is investigated as a support material for the NOx storage and reduction catalysts. The main aim is to increase the sulfur resistance.
The introduction of the dopants on the BaO (100) surface has increased the stability of the NO2 . The combination of local lattice strain and different oxidation state, which is obtained by the La doped BaO (100) surface, benefit both NO2 adsorption performance and sulfur tolerance. The binding energies of NO2 adsorption configurations over the alkali metal oxide (100) and (110) surfaces were higher than the binding energies of SO2 adsorption configurations. The stability of all of NO2 adsorption geometries on the alkali metal-loaded TiO2 (001) surface were higher than the stability of SO2 adsorption geometries. Increasing basicity enhanced the adsorption of NO2 molecule.
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Pearson, Stephen. "High oxidation state carbene complexes for C-H bond activation catalysis." Thesis, University of Edinburgh, 2010. http://hdl.handle.net/1842/7570.
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Chapter one is an introduction to the less common coordination and oxidation chemistry of palladium; complexes containing Pd-OR, Pd-NR2 and those in the oxidation states of +IV. An outline of PdII/IV catalysed ligand-directed oxidative functionalisation is also included. Chapter two covers the design and synthesis of a range of tethered N-heterocyclic carbene (NHC) complexes of Pd. In addition, the syntheses of a number of new tethered NHC ligands are described. The use of Density Functional Theory (DFT) to model the complexes in this thesis was explored. Chapter three describes the synthesis and characterisation of PdIV halide complexes. The relevance of these compounds to PdII/IV catalysed ligand-directed oxidative functionalisation is explored. DFT was used to probe the reaction pathway for N-bromosuccinimide and iodobenzene dichloride. Chapter four examines reactions with oxidants used to form C-O and C-C bonds. The reaction pathway for iodobenzene diacetate was investigated using DFT. Chapter five contains experimental details and characterising data for the compounds reported.
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Fredriksson, Tore. "Carbon Nanotubes : A Theoretical study of Young's modulus." Thesis, Karlstads universitet, Fakulteten för hälsa, natur- och teknikvetenskap (from 2013), 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-32351.
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Carbon nanotubes have extraordinary mechanical, electrical, thermal andoptical properties. They are harder than diamond yet exible, have betterelectrical conductor than copper, but can also be a semiconductor or evenan insulator. These ranges of properties of course make carbon nanotubeshighly interesting for many applications. Carbon nanotubes are already usedin products as hockey sticks and tennis rackets for improving strength and exibility. Soon there are mobile phones with exible screens made fromcarbon nanotubes. Also, car- and airplane bodies will probably be mademuch lighter and stronger, if carbon nanotubes are included in the construction.However, the real game changers are; nanoelectromechanical systems(NEMS) and computer processors based on graphene and carbon nanotubes.In this work, we study Young's modulus in the axial direction of carbonnanotubes. This has been done by performing density functional theorycalculations. The unit cell has been chosen as to accommodate for tubes ofdierent radii. This allows for modelling the eect of bending of the bondsbetween the carbon atoms in the carbon nanotubes of dierent radii. Theresults show that Young's modulus decreases as the radius decreases. Ineect, the Young's modulus declines from 1 to 0.8 TPa. This eect can beunderstood because the bending diminishes the pure sp^2 character of thebonds.These results are important and useful in construction, not only when usingcarbon nanotubes but also when using graphene. Our results point towardsa Young's modulus that is a material constant and, above a certain criticalvalue, only weakly dependent on the radius of the carbon nanotube.Graphene can be seen as a carbon nanotube with innite radius.
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Goel, Satyender. "DFT STUDY OF GEOMETRY AND ENERGETICS OF TRANSITION METAL SYSTEMS." Doctoral diss., University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2125.
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This dissertation focuses on computational study of the geometry and energetics small molecules and nanoclusters involving transition metals (TM). These clusters may be used for various industrial applications including catalysis and photonics. Specifically, in this work we have studied hydrides and carbides of 3d-transition metal systems (Sc through Cu), small nickel and gold clusters. Qualitatively correct description of the bond dissociation is ensured by allowing the spatial and spin symmetry to break. We have tested applicability of new exchange-correlation functional and alternative theoretical descriptions (spin-contamination correction in broken symmetry DFT and ensemble Kohn-Sham (EKS)) as well. We studies TM hydrides and carbides systems to understand the importance of underlying phenomenon of bond breaking in catalytic processes. We have tested several exchange-correlation functionals including explicit dependence on kinetic energy density for the description of hydrides (both neutral and cationic) and carbides formed by 3d-transition metals. We find M05-2x and BMK dissociation energies are in better agreement with experiment (where available) than those obtained with high level wavefunction theory methods, published previously. This agreement with experiment deteriorates quickly for other functionals when the fraction of the Hartree-Fock exchange in DFT functional is decreased. Higher fraction of HF exchange is also essential in EKS formalism, but it does not help when spin-adapted unrestricted approach is employed. We analyze the electron spin densities using Natural Bond Orbital population analysis and find that simple description of 3d electrons as non-bonding in character is rarely correct. Unrestricted formalism results in appreciable spin-contamination for some of the systems at equilibrium, which motivated us to investigate it further in details. In order to correct the spin contamination effect on the energies, we propose a new scheme to correct for spin contamination arising in broken-symmetry DFT approach. Unlike conventional schemes, our spin correction is introduced for each spin-polarized electron pair individually and therefore is expected to yield more accurate energy values. We derive an expression to extract the energy of the pure singlet state from the energy of the broken-symmetry DFT description of the low spin state and the energies of the high spin states (pentuplet and two spin-contaminated triplets in the case of two spin-polarized electron pairs). We validate our spin-contamination correction approach by a simple example of H2 and applied to more complex MnH system. Ensemble KS formalism is also applied to investigate the dissociation of C2 molecule. We find that high fraction of HF exchange is essential to reproduce the results of EKS treatment with exact exchange-correlation functional. We analyze the geometry and energetics of small nickel clusters (Ni2-Ni5) for several lowest energy isomers. We also study all possible spin states of small nickel cluster isomers and report observed trends in energetics. Finally we determine the geometry and energetics of ten lowest energy isomers of four small gold clusters (Au2, Au4, Au6, and Au8). We have also investigated the influence of cluster geometry, ligation, solvation and relativistic effects on electronic structure of these gold clusters. The effect of one-by-one ligand attachment in vacuum and solvent environment is also studied. Performance of five DFT functionals are tested as well; Local Spin Density Approximation (SVWN5), Generalized Gradient Approximation (PBE), kinetic energy density-dependent functional (TPSS), hybrid DFT (B3LYP), and CAM-B3LYP which accounts for long-range exchange effects believed to be important in the analysis of metal bonding in gold complexes and clusters. Our results exhibit the ligand induced stability enhancement of otherwise less stable isomers of Au4, Au6 and Au8. Ligands are found to play a crucial role in determining the 2D to 3D transition realized in small gold clusters. In order to select an appropriate theory level to use in this study, we investigate the effect of attachment of four different ligands (NH3, NMe3, PH3, PMe3) on cluster geometry and energetics of Au2 and Au4 in vacuum and in solution. Our results benchmark the applicability of DFT functional model and polarization functions in the basis set for calculations of ligated gold cluster systems. We employ five different basis sets with increasing amount of polarization and diffuse functions; LANL2DZ, LANL2DZ-P, def2-SVP, def2-TZVP, and def2-QZVP. We obtain NMe3 = NH3 < PH3 < PMe3 order of ligand binding energies and observe shallow potential energy surfaces in all molecules. Our results suggest appropriate quantum-chemical methodologies to model small noble metal clusters in realistic ligand environment to provide reliable theoretical analysis in order to complement experiments.Ph.D.
Department of Chemistry
Sciences
Chemistry PhD
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Lousada, Patrício Cláudio Miguel. "Reactions of aqueous radiolysis products with oxide surfaces : An experimental and DFT study." Doctoral thesis, KTH, Tillämpad fysikalisk kemi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-119780.
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The reactions between aqueous radiolysis products and oxide surfaces are important in nuclear technology in many ways. In solid-liquid systems, they affect (and at the same time are dependent on) both the solution chemistry and the stability of materials under the influence of ionizing radiation. The stability of surface oxides is a factor that determines the longevity of the materials where such oxides are formed. Additionally, the aqueous radiolysis products are responsible for corrosion and erosion of the materials. In this study, the reactions between radiolysis products of water – mainly H2O2 and HO radicals – with metal, lanthanide and actinide oxides are investigated. For this, experimental and computational chemistry methods are employed. For the experimental study of these systems it was necessary to implement new methodologies especially for the study of the reactive species – the HO radicals. Similarly, the computational study also required the development of models and benchmarking of methods. The experiments combined with the computational chemistry studies produced valuable kinetic, energetic and mechanistic data. It is demonstrated here that the HO radicals are a primary product of the decomposition of H2O2. For all the materials, the catalytic decomposition of H2O2 consists first of molecular adsorption onto the surfaces of the oxides. This step is followed by the cleavage of the O-O bond in H2O2 to form HO radicals. The HO radicals are able to react further with the hydroxylated surfaces of the oxides to form water and a surface bound HO• center. The dynamics of formation of HO• vary widely for the different materials studied. These differences are also observed in the activation energies and kinetics for decomposition of H2O2. It is found further that the removal of HO• from the system where H2O2 undergoes decomposition, by means of a scavenger, leads to the spontaneous formation of H2. The combined theoretical-experimental methodology led to mechanistic understanding of the reactivity of the oxide materials towards H2O2 and HO radicals. This reactivity can be expressed in terms of fundamental properties of the cations present in the oxides. Correlations were found between several properties of the metal cations present in the oxides and adsorption energies of H2O, adsorption energies of HO radicals and energy barriers for H2O2 decomposition. This knowledge can aid in improving materials and processes important for nuclear technological systems, catalysis, and energy storage, and also help to better understand geochemical processes.QC 20130322
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O'Kennedy, Sean James. "A kinetic and thermodynamic study of procyanidin oligomer conformation by 1H NMR and DFT." Thesis, Stellenbosch : Stellenbosch University, 2015. http://hdl.handle.net/10019.1/98054.
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Oftadeh, M., M. Gholamian, and H. H. Abdallah. "Investigation of Interaction Hydrogen Sulfide with (5,0) and (5,5) Single-Wall Carbon Nanotubes by DFT Method." Thesis, Sumy State University, 2012. http://essuir.sumdu.edu.ua/handle/123456789/35161.
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In the present study the interaction of Hydrogen Sulfide with inside and outside single-wall carbon
nanotube of (5,0) and (5,5) was investigated. This study was conducted using DFT at B3LYP/6-31G* level
of theory. Computational calculations were performed in the gaseous phase in Gaussian 09. The geometry
of all molecules under investigation was determined by optimizing all geometrical variables without any
symmetry constraints. The harmonic frequencies were computed from analytical derivatives for all species
in order to define the minimum-energy structures. The adsorption energies, the thermodynamic properties,
HOMO-LUMO energy gaps and partial charges of the interacting atoms were also studied during two rotation
kinds of H2S molecules vertical and horizontal to the main axes of nanotube.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35161
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Shojaee, Kambiz. "Fundamental aspects of ammonia oxidation on cobalt oxide catalysts." Thesis, The University of Sydney, 2014. http://hdl.handle.net/2123/13657.
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The current thesis deals with the ammonia oxidation on cobalt oxide catalyst at the molecular level. The catalytic oxidation of ammonia to NO is crucial in the industrial process of nitric acid production. Cobalt oxide catalysts are being used together with platinum gauzes to reduce the production cost and emission of greenhouse gas N2O. However, the fundamentals of ammonia oxidation on cobalt oxides are not known. This thesis aims to provide insights into our fundamental understanding of ammonia oxidation on Co3O4 surfaces. The performance of cobalt oxide catalysts in the oxidation of NH3 strongly depends upon the exposed surface terminations. Results indicate that different surfaces of Co3O4 behave markedly differently in oxidative reactions due to the difference in binding energy and O recombination energies and oxygen vacancy formation. Overall, NH3 oxidation follows stepwise dehydrogenative route (NH3* → NH2* → NH* → N*) on Co3O4 surfaces. Desorption of lattice products results in the formation of O vacancy sites opening the way for a Mars-van Krevelen mechanism. The successive dehydrogenation of ammonia preferably occurs on the surfaces exposing active lattice O sites. Removal of active lattice O sites from the Co3O4 surfaces in the form of products results in the surface reduction. If the rate of reduction is faster than that of re-oxidation, a CoO-like phase might form. The formation of CoO in Co3O4 catalysts during NH3 oxidation not only reduces the NH3 conversion but also alters the selectivity towards N2 rather than NO due to weak ability of lattice O at the CoO surface to assist the hydrogen abstraction process. A surface with a lower oxygen vacancy formation energy and a higher binding energy of hydrogen exhibits a higher activity towards ammonia oxidation to NO.
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Nelson, Lance Jacob. "Cluster Expansion Models Via Bayesian Compressive Sensing." BYU ScholarsArchive, 2013. https://scholarsarchive.byu.edu/etd/4032.
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The steady march of new technology depends crucially on our ability to discover and design new, advanced materials. Partially due to increases in computing power, computational methods are now having an increased role in this discovery process. Advances in this area speed the discovery and development of advanced materials by guiding experimental work down fruitful paths. Density functional theory (DFT)has proven to be a highly accurate tool for computing material properties. However, due to its computational cost and complexity, DFT is unsuited to performing exhaustive searches over many candidate materials or for extracting thermodynamic information. To perform these types of searches requires that we construct a fast, yet accurate model. One model commonly used in materials science is the cluster expansion, which can compute the energy, or another relevant physical property, of millions of derivative superstructures quickly and accurately. This model has been used in materials research for many years with great success. Currently the construction of a cluster expansion model presents several noteworthy challenges. While these challenges have obviously not prevented the method from being useful, addressing them will result in a big payoff in speed and accuracy. Two of the most glaring challenges encountered when constructing a cluster expansion model include:(i) determining which of the infinite number of clusters to include in the expansion, and (ii) deciding which atomic configurations to use for training data. Compressive sensing, a recently-developed technique in the signal processing community, is uniquely suited to address both of these challenges. Compressive sensing (CS) allows essentially all possible basis (cluster) functions to be included in the analysis and offers a specific recipe for choosing atomic configurations to be used for training data. We show that cluster expansion models constructed using CS predict more accurately than current state-of-the art methods, require little user intervention during the construction process, and are orders-of-magnitude faster than current methods. A Bayesian implementation of CS is found to be even faster than the typical constrained optimization approach, is free of any user-optimized parameters, and naturally produces error bars on the predictions made. The speed and hands-off nature of Bayesian compressive sensing (BCS) makes it a valuable tool for automatically constructing models for many different materials. Combining BCS with high-throughput data sets of binary alloy data, we automatically construct CE models for all binary alloy systems. This work represents a major stride in materials science and advanced materials development.
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Schultz, Spencer Albert. "An Investigation into the Use of Density Functional Theory (DFT) Calculations for Predicting Vibrational Transitions for Perfluroinated Sulfonic Acid (PFSA) Ionomer Membranes." Thesis, Virginia Tech, 2019. http://hdl.handle.net/10919/87470.
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Perfluorinated sulfonic acid (PFSA) ionomer membranes demonstrate great potential for use in proton exchange membrane fuel cells (PEMFCs) due to their favorable electronic properties and excellent efficiency. However, the assignment of key vibrational transitions such as the symmetric sulfonate and ether stretches is not yet fully understood depriving researchers of a quick and simple technique for analyzing morphological changes. The symmetric sulfonate stretch could be used to track changes in the ionic clusters formed within the membrane while the ether stretch will provide insight into the largely semi-crystalline PTFE phase. Alterations in either regime will affect both ion transport and mechanical properties and produce a major shift in device performance.
This study focused on predicting the vibrational transitions for Aquivion, 3M PFSA, and Nafion using density functional theory (DFT) with the bulk being performed using the same functional and basis set combination, B3LPY/6-31+G*. For all three ionomers, the predicted vibrational transitions were affected by changes in both the conformer and solvation method with water being used as the solvent. Despite the noted changes, both vibrational transitions were determined to be within the range of 970-1100 cm-1 with the symmetric sulfonate stretch present at around 970-1010 cm-1 and the ether stretch observed at around 1050-1100 cm-1 with solvation present. While the calculated peak positions mirror those found in the experimental spectra within the literature, the traditional normal mode assignments do not match those predicted by our calculations. However, recent studies have hypothesized that these vibrational transitions are coupled, which could explain why they have been so difficult to assign.Master of Science
Perfluorinated sulfonic acid (PFSA) ionomer membranes show great promise for use in proton exchange membrane fuel cells (PEMFCs) due to their excellent efficiency. However, the current techniques used to determine changes in structural configurations require sophisticated equipment and trained personnel to operate. Simpler techniques exist wherein the vibrations of certain bonds can be measured upon exposure of the sample to measured amounts of infrared light. The problem with this technique is that researchers currently do not fully understand at what wavelengths certain portions of the polymer known as functional groups will vibrate. These vibrations are also known as vibrational transitions. This study was undertaken to predict through numerical solutions to the Schrödinger equation at what wavelengths two particular vibrational transitions would occur for three common ionomers, Aquivion, 3M PFSA, and Nafion. For all three structures, the positions of these transitions mirrored that observed within the literature although the functional groups assigned to these positions did not match with those identified by our calculations. However, recent studies have indicated that these vibrational transitions occur at the same positions, which could explain why they have been so difficult to assign.
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Nardi, Lucas Marcelo Cavalari. "O modelo de Hubbard unidimensional via DFT: o potencial de troca e correlação e o funcional híbrido." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/76/76131/tde-21102016-102918/.
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A Teoria do funcional da Densidade (DFT) é muito empregada no estudo da densidade eletrônica e energia do estado fundamental de sistemas interagente de muitos elétrons. Uma de suas desvantagens é que, apesar de formalmente exata, a DFT depende de aproximações no funcional de troca e correlação Exc[n]. Uma de suas vantagens é a possibilidade de trabalhar com a conexão adiabática, que permite conectar explicitamente o sistema interagente de interesse com uma versão não-interagente de mesma densidade. Baseado em seu escopo esta dissertação tem como objetivo tratar da DFT no modelo de Hubbard unidimensional. Uma das vantagens em trabalhar com o Hubbard é a existência de uma solução formalmente exata para a energia do modelo homogêneo e unidimensional via ansatz de Bethe, tal solução serve de base para os nossos cálculos e resultados. Outra vantagem do modelo de Hubbard é a existência de um gap que aproximações usuais na DFT falham em reproduzir. Um de nossos resultados é calcular o gap de duas formas. Uma através da derivada da solução via ansatz de Bethe e outro é tratar o Hamiltoniano pela conexão adiabática, calcular o gap pelo potencial químico, este último calculado pelo ansatz de Bethe. Ao final comparamos a precisão dos métodos, apenas para descobrir que o método via potencial químico é mais preciso. Por último usamos a conexão adiabática e a aproximação de Hartree-Fock para teorizar um funcional híbrido no modelo de Hubbard unidimensional.The Density Functional Theory (DFT) is a widely used in the study of electronic density and energy of the ground-state of interacting systems consisting of many electrons. One of its disadvantages is that, although it is formally exact, the DFT depends on approximations of the exchange-correlation functional Exc[n]. One of its advantages consists of the possibility of working with the adiabatic connection, which allows a explicit connection between the interacting system of our interest and a non-interacting system that yields the same density. Based on its scope this dissertation aims to address the DFT in the one-dimensional Hubbard model. One of the Hubbards model advantage consists of the existence of a formally exact solution to the energy of the homogeneous one-dimensional model via Bethe ansatz, such a solution serves as the basis for our calculations and results. Anothe Hubbards model advantage is the existence of a gap that usual approximations in DFT fail to calculate. One of our results is to calculate the gap in two different ways. One through the derivative of the Bethe ansatz solution and the other is to address the Hamiltonian through the adiabatic connection, calculate the gap through the chemical potential, the latter calculated via Bethe ansatz. In the end we compare their precisions, only to find that the one via chemical potential is more precise. At last we use the adiabatic connection and the Hartree-Fock approximation to theorize a hybrid functional in the one-dimensional Hubbard model.
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Arvidsson, Igor. "Theoretical Investigations of Boron Related Materials Using DFT." Doctoral thesis, Uppsala University, Department of Materials Chemistry, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-7889.
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In the history of Chemistry, materials chemists have developed their ideas mainly by doing experiments in laboratories. The underlying motivation for this laboratory work has generally been pure curiosity or the ambition to find a solution to a specific problem. Minor changes in the composition or structure of a material can cause major changes in its properties. The development of powerful computers has now opened up the possibility to calculate properties of new materials using quantum mechanical methods.
The Chemistry of different boron-related materials has been evaluated in this thesis by Density Functional Theory (DFT). Cubic boron nitride (c-BN) is a most interesting material for the microelectronics and tool industry. During thin film deposition of c-BN, several problems arise which most often result in unwanted BN isomorphs. Chemical processes at the (110) and (111) surface of c-BN have been investigated in order to shed light upon some of these complex processes. Typically adsorption energies and surface reconstruction were found to differ significantly between the two surfaces.
Other materials investigated are layered transition-metal diborides (MeB2). Incorporation of transition-metal atoms into elemental boron in its most fundamental structure, ά-boron, has also been investigated. The calculations on MeB2 focused on the stability of the planar compared to the puckered structure of MeB2. Stability was investigated by calculating Density of States (DOS) and bond populations. Deviations in the cell parameters from their ideal values were also considered.
A separate project concerned reactivity of the TiB2(001) surface. Molecular and dissociated adsorption energies and adsorption geometries were calculated for H2, H2O and O2. It was concluded that the titanium surface was more reactive than the boron surface and that the adsorption energies were comparable to or stronger than other well known surface-active compounds like TiO2.
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Agenet, Nicolas. "Synthèse de composés polycycliques silylés : étude DFT de la cycloaddition [2 + 2 +2] des alcynes et de la cocyclisation 2:1 d'alcynes et d'alcènes catalysées par des complexes du cobalt." Paris 6, 2007. http://www.theses.fr/2007PA066276.
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Le but de cette thèse est le développement d'une méthode de formation de composés polycycliques silylés. L'insertion régiosélective d'une entité CpCo(CO) dans la liaison Csp2–Si d'un benzosilacyclobutène a permis d'isoler un cobaltasilabenzocyclopentène. Mis en présence d'insaturations tels que des alcynes ou des alcènes, il se forme un composé bicyclique silylé. Une version intramoléculaire a été développé à partir d'un benzosilacyclobutène présentant une chaîne portant une insaturation, diverses structures tricycliques ont ainsi été synthétisées. Une étude DFT sur le mécanisme de la réaction a été menée. Elle inclue les géométries où se produisent les changements de spin des intermédiaires réactionnels. En marge de cette étude, les mêmes techniques de calculs ont été utilisées pour mettre au jour un mécanisme de la cycloaddition [2+2+2] des alcynes rendant compte de la réactivité particulière des alcynes appauvris en électrons. D'autre part, le mécanisme de la cocyclisation 2:1 d'alcynes et d'alcènes a été étudié.
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Demiroglu, Ilker. "Ab Initio Studies Of Pentacene On Ag(111) Surfaces." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/2/12611425/index.pdf.
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In this work pentacene adsorption on both flat and stepped Ag(111) surfaces were investigated by using Density Functional Theory within Projected Augmented Wave method. On the flat Ag(111) surface favorable adsorption site for a single pentacene molecule was determined to be the bridge site with an angle of 60◦
between pentacene molecular long axis and [011] lattice direction. Potential energy surface was found to be flat, especially along lattice directions. Diffusion and rotation barriers for pentacene on this surface were found to be smaller than 40 meV indicating the possibility of a two dimensional gas phase. Calculated adsorption energies for the flat surface indicate a weak interaction between molecule and the surface indicating physisorption. On the flat surface monolayer case is found to have lower adsorption energy than the isolated case due to pentacene&
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pentacene interactions. On the stepped Ag(233) surface, close to the step edge, adsorption energy increased significantly due to the stronger interaction between pentacene molecule and low coordinated silver step atoms. On the terraces of this surface, far from step edges, however a flat potential energy surface was observed similar to the case of flat Ag(111) surface. On the stepped surface pentacene found its favorable configuration as parallel to the step with a tilt angle similar to the observed thin film phase of pentacene on Ag(111) surface. Pentacene molecule showed small distortions on stepped surface and are closer to the silver step atoms 1 Å
more than the case of flat surface, hinting a chemical interaction as well as van der Waals interactions. However on Ag(799) surface, the perpendicular orientation of the pentacene molecule to the step direction showed no strong interaction due to less matching of carbon atoms with silver step atoms.
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Hansson, Anders. "Electronic Structure and Transport Properties of Carbon Based Materials." Doctoral thesis, Linköpings universitet, Beräkningsfysik, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-7544.
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In the past decade the interest in molecular electronic devices has escalated. The synthesis of molecular crystals has improved, providing single crystals or thin films with mobility comparable with or even higher than amorphous silicon. Their mechanical flexibility admits new types of applications and usage of electronic devices. Some of these organic crystals also display magnetic effects. Furthermore, the fullerene and carbon nanotube allotropes of carbon are prominent candidates for various types of applications. The carbon nanotubes, in particular, are suitable for molecular wire applications with their robust, hollow and almost one-dimensional structure and diverse band structure. In this thesis, we have theoretically investigated carbon based materials, such as carbon nanotubes, pentacene and spiro-biphenalenyl neutral radical molecular crystals. The work mainly deals with the electron structure and the transport properties thereof. The first studies concerns effects and defects in devices of finite carbon nanotubes. The transport properties, that is, conductance, are calculated with the Landauer approach. The device setup contains two metallic leads attached to the carbon nanotubes. Structural defects as vacancies and bending are considered for single-walled carbon nanotubes. For the multi-walled carbon nanotubes the focus is on inter-shell interaction and telescopic junctions. The current voltage characteristics of these systems show clear marks of quantum dot behaviour. The influence of defects as vacancies and geometrical deformations are significant for infinite systems, but in these devices they play a minor role. The rest of the studies concern molecular crystals, treated with density-functional theory (DFT). Inspired by the enhance of the electrical conductivity obtained experimentally by doping similar materials with alkali metals, calculations were performed on bundles of single-walled carbon nanotubes and pentacene crystals doped with potassium. The most prominent effect of the potassium intercalation is the shift of Fermi level in the nanotube bands. A sign of charge transfer of the valence electrons of the potassium atoms. Semi-conducting bundles become metallic and metallic bundles gain density of states at the Fermi level. In the semi-conducting pristine pentacene crystals structural transitions occur upon doping. The herringbone arrangement of the pristine pentacene molecules relaxes to a more π-stacked structure causing more dispersive bands. The charge transfer shifts the Fermi level into the lowest unoccupied molecular orbital band and turns the crystal metallic. Finally, we have studied molecular crystals of spiro-biphenalenyl neutral radicals. According to experimental studies, some of these materials show simultaneous electrical, optical and magnetical bistability. The electronic properties of these crystals are investigated by means of DFT with a focus on the possible intermolecular interactions of radical spins.
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Hollandsworth, Carl B. "Full and half sandwich compounds of dimolybdenum and ditungsten." The Ohio State University, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=osu1095455882.
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Kvashnin, Yaroslav. "Ab initio theory of ferromagnetic transition metals and alloys under high pressure." Thesis, Grenoble, 2013. http://www.theses.fr/2013GRENY032/document.
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Le sujet de cette thèse porte sur l'étude des propriétés magnétiques de métaux de transition et leurs alliages sous haute pression au moyen de calculs ab initio. D'abord, les résultats de mesures de dichroïsme magnétique circulaire des rayons X (XMCD) au seuil K du nickel et du cobalt sont interprétés. Je montre que les données expérimentales doivent être comparées à celle de l'aimantation d'orbite projetée sur les états ``p''. Je mets en avant que la pression affecte différemment le spin et le moment orbitalaire. Dans le cas de l'alliage FeCo, la transition structurelle s'effectue sous une pression appliquée de l'ordre de 35 GPa. Je propose que l'émergence de l'antiferromagnétisme peut expliquer la disparition du signal XMCD au seuil K du fer et du cobalt. Ensuite, la transformation de phase dans FePd3, induite sous une pression de 12 GPa, est étudiée. Je démontre que le système est décrit par un modèle de Heisenberg étendu, contenant interactions d'échange biquadratiques forts. Selon nos résultats, FePd3 subit une transition de l'etat ferromagnétique à l'état triple-Q non-colinéaire, lorsqu'il est compressé. Enfin, une mise en oeuvre du tenseur des contraintes dans le code BigDFT est présentée. Il est montré qu'un traitement explicite des électrons de coeur permet de réduire considérablement les erreurs introduites par les pseudo-potentiels. Ainsi, les estimations des propriétés structurales peuvent être amélioréesThe subject of the present thesis is the investigation of magnetic properties of transition metals and their alloys under high pressure by means of first-principles calculations. First, the results of the K-edge x-ray magnetic circular dichroism (XMCD) experiments on Ni and Co are interpreted. It is shown that the experimental pressure evolution of the data should be compared with that of the p-projected orbital magnetization. I emphasize that the spin and orbital moments have different behavior upon compression. In the case of FeCo alloy the structural transition occurs under the pressure of 35 GPa. I propose that the emergence of antiferromagnetism can explain the disappearance of the XMCD signal at the Fe and Co K-edges. Then, the phase transformation in FePd3 , induced under pressure of 12 GPa, is investigated. I demonstrate that the system is described by an extended Heisenberg model, containing strong biquadratic exchange interactions. According to the results, FePd3 undergoes a transition from the ferromagnetic to the noncollinear triple-Q state when compressed. Finally, the implementation of the stress tensor in the BigDFT software package is presented. It is shown that an explicit treatment of core electrons can considerably reduce the errors introduced by the pseudopotentials. Thus the estimates of the structural properties can be improved
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Marut, Clotilde. "La théorie de la fonctionnelle de la densité d'ensemble : une alternative pour décrire les états excités et pour pallier aux limitations des méthodes ab initio standard." Electronic Thesis or Diss., Toulouse 3, 2023. http://www.theses.fr/2023TOU30312.
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Au cours des dernières décennies, la théorie de la fonctionnelle de la densité (DFT) s'est imposée comme une approche rigoureuse pour la description de l'état fondamental des systèmes électroniques. Grâce à son faible coût computationnel et à l'élaboration d'approximations sophistiquées pour la fonctionnelle d'échange-corrélation (xc-DFA), la DFT est devenue la méthode de choix pour le calcul de structure électronique. Néanmoins, il subsiste nombre de défis que la DFT ne parvient pas à surmonter. En réalité, ces carences ne sont pas le fruit de la théorie elle-même mais plutôt du fait de défauts intrinsèques des approximations utilisées. Il existe une formulation plus générale de la DFT pour les nombres fractionnaires d'occupation qui permet la description de systèmes avec nombre fractionnaire d'électrons, la PPLB-DFT. Cette formulation grand canonique de la DFT peut être mise en place à l'aide d'un formalisme d'ensemble et permet une extraction directe d'énergies d'excitation chargée et d'autres propriétés à partir d'un seul calcul de type DFT. Malheureusement, l'incapacité des DFAs à reproduire la fameuse dérivée discontinue (DD) s'est avérée être particulièrement préjudiciable pour la prédiction d'énergies d'excitation chargée, telles que les potentiels d'ionisation et les affinités électroniques, donnant lieu à des erreurs conséquentes, et connue comme le problème du gap fondamental. Dans ce contexte, la DFT d'ensemble (eDFT) offre une alternative très attrayante du fait de sa capacité à user de DFAs dépendantes du poids de l'ensemble pour reproduire la DD via leur dérivée. La DFT est connue pour montrer des limites vis-à-vis du calcul d'énergies d'excitation chargée et neutre. La procédure standard pour accéder aux états excités neutralement dans le cadre de la DFT est à travers son extension dépendante du temps, la TD-DFT. En effet, l'usage est de recourir à la TD-DFT pour obtenir des prédictions acceptables pour les énergies de transition des niveaux excités les plus bas, cela avec un coût computationnel relativement modéré. Bien que la TD-DFT se soit avérée incroyablement fructueuse pour accéder aux énergies d'excitation neutre, elle a également montré certaines limites lors de la description de certains phénomènes et propriétés physiques. En cela, l'eDFT constitue une alternative prometteuse à la TD-DFT pour le calcul des énergies d'excitation électroniques. En eDFT, il est possible d'extraire n'importe quelle énergie d'excitation neutre d'un système électronique en un seul calcul à l'aide d'un ensemble Gross-Oliveira-Kohn (GOK), et cela avec un coût computationnel et un niveau d'approximation pour la fonctionnelle d'xc, similaires à ceux de la DFT standard. La GOK-DFT est une alternative moins connue mais tout autant rigoureuse que la TD-DFT, où le large choix de poids de l'ensemble et la dépendance en poids de la fonctionnelle xc peuvent significativement influer sur la qualité des énergies calculées. En temps normal, accéder aux énergies d'excitation chargée nécessite de faire varier le nombre d'électrons du système, ce qui peut s'avérer problématique dans certains cas. Très récemment, un nouveau formalisme canonique a été développé, l'eDFT N-centrée, rendant possible l'extraction d'énergies d'excitation chargée sans altération du nombre d'électrons. Le comportement des DFAs standard dans le cadre de l'eDFT peut offrir une compréhension plus poussée de la nature intrinsèque des erreurs systématiques dont elles souffrent, telles que la violation des conditions exactes de linéarité par morceaux et de constance de l'énergie. En outre, la mauvaise description des systèmes avec charge et spin fractionnaires a prouvé avoir un impact majeur dans la description des systèmes fortement corrélés ainsi que dans les processus de dissociation et la prédiction de gaps d'énergie. Tout cela pourrait donner un nouvel essor au développement futur de la DFT et à des applications émergentes jusqu'alors inaccessiblesOver the last few decades, density-functional theory (DFT) has proved to be a rigorous approach for describing the ground-state of any electronic system. Due to a relatively low computational cost and the elaboration of sophisticated density-functional approximations (DFAs), DFT became the prevailing method used in electronic-structure calculations. Still, there remain numerous challenges that standard DFAs fail to overcome. These limitations are not attributed to failures of the theory itself but are rather due to deficiencies of the currently used approximate exchange-correlation (xc) functionals. There exists a generalization of ground-state DFT to fractional occupation numbers which allows for the description of systems with fractional number of electrons, PPLB-DFT. Such grand canonical extension of DFT can be achieved through the use of the ensemble formalism and enables direct extraction of charged excitation energies and other properties from a single DFT-like calculation. Unfortunately, the inability of commonly used exchange-correlation DFAs to mimic the infamous derivative discontinuity (DD) has proved to be highly detrimental to the prediction of charged excitations such as ionization potentials and electron affinities, yielding substantial errors, and known as the fundamental-gap problem. Regarding this matter, ensemble DFT (eDFT) offers a very appealing alternative benefiting from the possibility for explicitly weight-dependent xc-functionals to mimic the infamous DD through their derivatives with respect to the ensemble weights. DFT is known to possess deficiencies when it comes to computing charged and neutral excitations. The most popular way to access neutrally excited states within the scope of DFT is through its time-dependent extension, TD-DFT. Indeed, one would usually turn to TD-DFT to get accurate transition energies for low-lying excited-states with a relatively moderate computational cost. Although TD-DFT has been incredibly successful to access neutral excitation energies, it still suffers from some limitations and fails to provide accurate descriptions of some phenomena and properties. eDFT constitutes a promising alternative to TD-DFT for computing electronic excitation energies. In eDFT, it is possible to extract any neutral excitation energies of a N-electron system from a single calculation through the use of a Gross-Oliveira-Kohn (GOK) ensemble, with a similar computational cost and level of approximation for the xc-functional than in an usual DFT calculation. GOK-DFT is a less well-known but comparably rigorous alternative to TD-DFT where the large choice of ensemble weights and the weight-dependence of DFAs can significantly impact the accuracy of the energies. In DFT, it is well-known that the HOMO-LUMO gap can be a very poor estimation of the fundamental gap of the system, whereas eDFT may provide better predictions. Nevertheless, accessing charged excitations usually require to vary the number of electrons of the system, which can be problematic for some systems. Very recently, a new canonical eDFT formalism has been developed, the N-centered formalism, which allows for the extraction of charged excitation energies without any alteration of the number of electrons of the system. The behaviour of standard approximations in the scope of eDFT may provide additional insight into the intrinsic systematic errors of DFAs, such as the violation of the piecewise-linearity and constancy-condition exact properties. Indeed, poor descriptions of systems with fractional charges and fractional spins have shown to have major implications on the description of strongly correlated systems, which are known to suffer from large static-correlation errors, as well as on the prediction of asymptotic integer dissociations and band-gap predictions. These considerations may lead the way to further development and refinement of the DFT scheme towards both current and emerging applications
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Silva, Josà JÃnior Alves da. "AdsorÃÃo de Ãtomos alcalinos e halogÃnios em uma superfÃcie de Grafeno: um estudo de primeiros princÃpios." Universidade Federal do CearÃ, 2008. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=1770.
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Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgicoO grafeno à atualmente o tÃpico mais corrente em fÃsica da materia condensada e ciÃncia dos materiais e foi isolado pela primeira vez a menos de quatro anos. O grafeno tem sido proposto como um material alternativo aos nanotubos de carbono em diversas aplicaÃÃes, devido a sua fÃcil sintetizaÃÃo e seu baixo custo. A fim de explorar uma potencial aplicaÃÃo dessas nanoestruturas em dispositivos eletrÃnicos, atravÃs de cÃlculos de primeiros princÃpios baseados na teoria do funcional da densidade, estudamos a interaÃÃo entre uma superfÃcie de grafeno e Ãtomos alcalinos (Li, Na e K) e halogÃnios (Cl, I e I2). Verificamos que a adsorÃÃo desses Ãtomos na superfÃcie do grafeno provoca significativas modificaÃÃes na estrutura eletrÃnica do grafeno. Observamos uma grande transferÃncia de carga entre os Ãtomos alcalinos (halogÃnios) e a superfÃcie do grafeno. Essas transferÃncias foram da ordem de 0,65-0,85 e- dos Ãtomos alcalinos para o grafeno e 0,37 (0,27) e- do grafeno para o Ãtomo de cloro (iodo). Os metais alcalinos apresentaram uma maior estabilidade sobre o centro de um hexÃgono do grafeno, tendo energias de ligaÃÃo entre -1,47 e -1,03 eV, onde a ordem de intensidade à dada por Li > K > Na. Essa predisposiÃÃo por um sÃtio especÃfico nÃo foi observada para os dois halogÃnios estudados. O Ãtomo de cloro apresentou uma maior estabilidade quando adsorvido sobre um Ãtomo da superfÃcie do grafeno, com energia de ligaÃÃo da ordem de 0,98 eV, no entanto, isso nÃo foi visto no caso do Ãtomo de iodo onde energias de ligaÃÃo equivalentes para todos os sÃtios estudados foram encontradas da ordem de 0,42 eV. A molÃcula I2 tambÃm nÃo apresentou uma predileÃÃo por uma sitio especÃfico da superfÃcie do grafeno, mas mostrou-se mais estÃvel quando adsorvida com seu eixo perpendicular ao plano do grafeno.
Graphene is currently the hottest topic in condensed-matter physics and materials science and was isolated less than four years ago. Graphene layers have been proposed as alternative materials for replacing carbon nanotubes in some applications, due to its easy synthesis and low costs. In order to explore potential applications of those nanostructures in electronic devices, through first principles based on the density functional theory, we studied the interaction between graphene surface and alkaline (Li, Na and K) and halogens (Cl, I and I$_2$ ) atoms. We verified that the adsorption of these atoms on the graphene surface cause significant modifications in the graphene electronic structure. We observed a large charge transfer between the alkaline (halogens) atoms and graphene surface. These charge transfers were found to be 0,65 - 0,85 e- from the alkaline atoms to graphene and 0,37 (0,27) e- from the graphene to chlorine (iodine) atoms. The alkaline atoms presented a larger stability on the center of one of the graphene hexagons, presenting binding energy in the range -1, 47 and -1, 03 eV, where the order of intensity is given by Li > K > Na. This predisposition for a specific site was not observed for the twostudied halogens. The chlorine atom present the larger stability when adsorbed on a top atom of the graphene surface with binding energy about 0, 98 eV, however this behavior was not be seen in the iodine atom case where equivalent binding energies for all the studied sites were found to be about 0,42 eV. The I2 molecule also does not present predilection for a specific site on the graphene surface, however it showed more stable when adsorbed with its axis perpendicular to the graphene surface plane.
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Silva, José Júnior Alves da. "Adsorção de átomos alcalinos e halogênios em uma superfície de Grafeno: um estudo de primeiros princípios." reponame:Repositório Institucional da UFC, 2008. http://www.repositorio.ufc.br/handle/riufc/8058.
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SILVA, José Júnior Alves da. Adsorção de átomos alcalinos e halogênios em uma superfície de Grafeno: um estudo de primeiros princípios. 2008. 85 f. Dissertação (mestrado) - Programa de Pós-Graduação em Física, Departamento de Física, Centro de Ciências, Universidade Federal do Ceará, Fortaleza, 2008.Submitted by Edvander Pires (edvanderpires@gmail.com) on 2014-05-13T22:42:26Z No. of bitstreams: 1 2008_dis_jjasilva.pdf: 4132276 bytes, checksum: 961eed37504f3bed4fe8ed917e245554 (MD5)
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Graphene is currently the hottest topic in condensed-matter physics and materials science and was isolated less than four years ago. Graphene layers have been proposed as alternative materials for replacing carbon nanotubes in some applications, due to its easy synthesis and low costs. In order to explore potential applications of those nanostructures in electronic devices, through first principles based on the density functional theory, we studied the interaction between graphene surface and alkaline (Li, Na and K) and halogens (Cl, I and I$_2$ ) atoms. We verified that the adsorption of these atoms on the graphene surface cause significant modifications in the graphene electronic structure. We observed a large charge transfer between the alkaline (halogens) atoms and graphene surface. These charge transfers were found to be 0,65 - 0,85 e- from the alkaline atoms to graphene and 0,37 (0,27) e- from the graphene to chlorine (iodine) atoms. The alkaline atoms presented a larger stability on the center of one of the graphene hexagons, presenting binding energy in the range -1, 47 and -1, 03 eV, where the order of intensity is given by Li > K > Na. This predisposition for a specific site was not observed for the twostudied halogens. The chlorine atom present the larger stability when adsorbed on a top atom of the graphene surface with binding energy about 0, 98 eV, however this behavior was not be seen in the iodine atom case where equivalent binding energies for all the studied sites were found to be about 0,42 eV. The I2 molecule also does not present predilection for a specific site on the graphene surface, however it showed more stable when adsorbed with its axis perpendicular to the graphene surface plane.
O grafeno é atualmente o tópico mais corrente em física da materia condensada e ciência dos materiais e foi isolado pela primeira vez a menos de quatro anos. O grafeno tem sido proposto como um material alternativo aos nanotubos de carbono em diversas aplicações, devido a sua fácil sintetização e seu baixo custo. A fim de explorar uma potencial aplicação dessas nanoestruturas em dispositivos eletrônicos, através de cálculos de primeiros princípios baseados na teoria do funcional da densidade, estudamos a interação entre uma superfície de grafeno e átomos alcalinos (Li, Na e K) e halogênios (Cl, I e I2). Verificamos que a adsorção desses átomos na superfície do grafeno provoca significativas modificações na estrutura eletrônica do grafeno. Observamos uma grande transferência de carga entre os átomos alcalinos (halogênios) e a superfície do grafeno. Essas transferências foram da ordem de 0,65-0,85 e- dos átomos alcalinos para o grafeno e 0,37 (0,27) e- do grafeno para o átomo de cloro (iodo). Os metais alcalinos apresentaram uma maior estabilidade sobre o centro de um hexágono do grafeno, tendo energias de ligação entre -1,47 e -1,03 eV, onde a ordem de intensidade é dada por Li > K > Na. Essa predisposição por um sítio específico não foi observada para os dois halogênios estudados. O átomo de cloro apresentou uma maior estabilidade quando adsorvido sobre um átomo da superfície do grafeno, com energia de ligação da ordem de 0,98 eV, no entanto, isso não foi visto no caso do átomo de iodo onde energias de ligação equivalentes para todos os sítios estudados foram encontradas da ordem de 0,42 eV. A molécula I2 também não apresentou uma predileção por uma sitio específico da superfície do grafeno, mas mostrou-se mais estável quando adsorvida com seu eixo perpendicular ao plano do grafeno.