Dissertations / Theses: 'Exchange energy functional'

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Khorashad, Arash Sorouri. "Investigation of the exchange energy density functional." Thesis, Imperial College London, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.504765.

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Density Functional Theory (DFT) is an important tool in the treatment of quantum many-body problems. In spite of being exact in principle, the application of DFT requires the use of approximations, because it involves an unknown universal functional called the exchange-correlation energy. In this thesis we describe an accurate and efficient extension of Chawla and Voth's planewave based algorithm for calculating exchange energies, exchange energy densities, and exchange energy gradients with respect to wave function parameters in systems of electrons subject to periodic boundary conditions. The theory and numerical results show that the computational effort scales almost linearly with the number of plane waves and quadratically with the number of k vectors. To obtain high accuracy with relatively few k vectors, we use an adaptation of Gygi and Baldereschi's method for reducing Brillouin zone integration errors. We then generate a large database of highly accurate exchange energy densities in 106 artificial but realistic solid-state systems. We use the database not only to examine the accuracy of some important existing exchange functionals, but also to show that there exists a smooth function of the local electron density, its gradient and Laplacian that fits our data well. We also study the effects of twist-averaging on the finite-size errors in the exchange energy of a uniform electron gas, using the Ewald, model periodic Coulomb (MPC) and screened Coulomb interactions. In the case of the Ewald interaction, this investigation is carried out in both the canonical (fixed particle number) and grand-canonical (fixed Fermi wave vector) ensembles. Finally, we study the new reciprocal-space approach to the . Coulomb finite-size errors introduced by Chiesa et al. and find that it is almost equivalent to the use of the MPC interaction.

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Tsutsui, Yuko. "EXPLORING FUNCTIONAL AND FOLDING ENERGY LANDSCAPES BY HYDROGEN-DEUTERIUM EXCHANGE MASS SPECTROMETRY." Case Western Reserve University School of Graduate Studies / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=case1196199391.

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Sanchez-Friera, Paula. "Total energy calculations from self-energy models." Thesis, University of York, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.369299.

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Armiento, Rickard. "The many-electron energy in density functional theory : from exchange-correlation functional design to applied electronic structure calculations." Doctoral thesis, Stockholm : AlbaNova Universitetscentrum, Skolan för Teknikvetenskap, Kungliga Tekniska högskolan, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-428.

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Odashima, Mariana Mieko. "Análise e aplicação do limite de Lieb-Oxford na teoria do funcional da densidade." Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/76/76131/tde-14062010-164125/.

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Simulações de propriedades de estrutura eletrônica possuem fundamental importância para a física do estado sólido e química quântica. A teoria do funcional da densidade (DFT) é atualmente o método de estrutura eletrônica mais empregado, desde escalas atômicas e nanoscópicas até aglomerados biomoleculares. A acurácia da DFT depende essencialmente de aproximações para os efeitos de troca e correlação, para as quais existem vínculos a serem satisfeitos como forma de controlar sua construção. Esse é um tópico de grande importância, pois a construção de melhores funcionais é necessária para uma descrição cada vez mais precisa dos efeitos de muitos corpos na DFT. No presente trabalho, investigamos o comportamento da energia de troca e correlação e o desenvolvimento de funcionais aproximados sob a ótica de um vínculo universal de sistemas de interação Coulombiana, o limite inferior de Lieb-Oxford. Primeiramente apresentamos evidências de que em diversas classes de sistemas a energia de troca e correlação é distante do limite de Lieb-Oxford. A redução do limite foi implementada nos funcionais Perdew-Burke-Erzenhof (PBE), porém a forma com que o vínculo é implementado apenas aumentou a energia de troca. Propusemos em seguida que o limite de Lieb-Oxford não fosse utilizado apenas para determinar o valor de um parâmetro, como em PBE, mas que fosse ponto-de-partida de uma nova forma família de funcionais, do tipo hiper-GGA. Exploramos uma construção não-empírica, com implementação pós-autoconsistente. A particular forma proposta se beneficiou da redução do limite Lieb-Oxford, obtendo resultados satisfatórios para as energias de correlação.
Electronic-structure calculations play a fundamental role in solid-state physics and quantum chemistry. Density-functional theory (DFT) is today the most-widely used electronic-structure method, from atomic and nanoscopic scales to biomolecular aggregates. The accuracy of DFT depends essentially on approximations to the exchange and correlation energy, which are controlled by exact constraints. This is a very important issue, since the improvement of functionals is the key to a better description of many-body effects. In the present work, we investigate the exchange-correlation energy and approximate functionals from the viewpoint of an universal constraint on interacting Coulomb systems: the Lieb-Oxford lower bound. Initially we present evidence that for several classes of systems (atoms, ions, molecules and solids), the actual exchange-correlation energies are far from the Lieb-Oxford lower bound. A tighter form of this bound was conjectured; implemented in the Perdew-Burke-Erzenhof (PBE) functionals, and tested for atoms, molecules and solids. Finally, we propose to use the Lieb-Oxford bound not just to fix the value of a parameter as in PBE, but as a starting point for a new family of hyper-GGA functionals. For these, we explored a non-empirical construction, investigating its performance for atoms and small molecules post-selfconsistently. The particular HGGA proposed benefited from the tightening of the Lieb-Oxford bound and exhibited satisfactory correlation energies.

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Schweinefuß, Maria E., Sergej Springer, Igor A. Baburin, Todor Hikov, Klaus Huber, Stefano Leoni, and Michael Wiebcke. "Zeolitic imidazolate framework-71 nanocrystals and a novel SOD-type polymorph: solution mediated phase transformations, phase selection via coordination modulation and a density functional theory derived energy landscape." Royal Society of Chemistry, 2014. https://tud.qucosa.de/id/qucosa%3A36102.

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We report a rapid additive-free synthesis of nanocrystals (NCs) of RHO-type ZIF-71 (1) of composition [Zn(dcim)₂] (dcim = 4,5-dichloroimidazolate) in 1-propanol as solvent at room temperature. NC-1 has a size of 30–60 nm and exhibits permanent microporosity with a surface area (SBET = 970 m² g−¹) comparable to that of microcrystalline material. When kept under the mother solution NC-1 undergoes transformation into a novel SOD-type polymorph (2), which in turn converts into known ZIF-72 (3) with lcs topology. It is shown that microcrystals (MCs) of 2 can be favourably synthesised using 1-methylimidazole as a coordination modulator. NC-2 with size <200 nm was prepared using NC-ZIF-8 as a template with SOD topology in a solvent assisted ligand exchange-related process. DFT-assisted Rietveld analysis of powder XRD data revealed that novel polymorph 2 possesses an unusual SOD framework conformation. 2 was further characterised with regard to microporosity (SBET = 597 m² g−¹) and thermal as well as chemical stability. DFT calculations were performed to search for further potentially existing but not-yet synthesised polymorphs in the [Zn(dcim)₂] system.

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Morbec, Juliana Maria Abreu da Silva. "Magnetismo orbital em sistemas de muitos elétrons." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/76/76131/tde-26032009-150954/.

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Neste trabalho investigamos os efeitos do magnetismo orbital sobre o gás de elétrons tridimensional e sobre íons de camadas abertas em matrizes metálicas. Derivamos uma expressão analítica fechada para a energia de troca do gás de elétrons tridimensional na presença de fortes campos magnéticos, incluindo contribuições do segundo nível de Landau e polarização de spin arbitrária. Esse cálculo generaliza e corrige resultados anteriores disponíveis na literatura. Em seguida, realizamos um cálculo numérico da energia de troca do gás de elétrons tridimensional na presença de campos magnéticos, permitindo a ocupação de um número ilimitado de níveis de Landau, possibilitando assim a obtenção da energia de troca para quaisquer valores de campo magnético e densidade. Em uma abordagem independente, usamos as aproximações de Thomas-Fermi e Thomas-Fermi-Dirac para construir modelos simples para a função dielétrica do gás de elétrons tridimensional no regime de campos magnéticos muito fortes (apenas o primeiro nível de Landau ocupado). Finalmente, estabelecemos vínculos entre os tratamentos fenomenológicos e de primeiros princípios do magnetismo orbital em íons de camadas abertas em matrizes metálicas. Esses vínculos forneceram um embasamento teórico para o uso dos termos de polarização orbital em cálculos Kohn-Sham e levaram à obtenção de expressões aproximadas para os funcionais de troca-correlação da teoria do funcional da densidade de corrente.
In this work, we investigate the effects of orbital magnetism in the three-dimensional electron gas and in open-shell ions in a solid. We derive a closed analytical expression for the exchange energy of the three-dimensional electron gas in strong magnetic fields including the contribution of the second Landau level and arbitrary spin polarization. This calculation generalizes and corrects earlier results available in the literature. Next, we perform a numerical calculation of the exchange energy of the three-dimensional electron gas in a magnetic field, allowing several Landau levels to be occupied, to obtain the exchange energy for arbitrary values of magnetic field and density. In an independent approach, we use the Thomas-Fermi and Thomas-Fermi-Dirac approximations to construct simple model dielectric functions for the three-dimensional electron gas in the strong magnetic field regime (where only the lowest Landau level is occupied). Finally, we establish links between the phenomenological and the first-principles treatment of orbital magnetism in open-shell ions in solids. These links provide a theoretical foundation for the use of orbital polarization terms in Kohn-Sham calculations and allow to obtain approximations to the exchange-correlation functionals of current-density functional theory.

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Olovsson, Weine. "Influence of Global Composition and Local Environment on the Spectroscopic and Magnetic Properties of Metallic Alloys." Doctoral thesis, Uppsala University, Department of Physics, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-5823.

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Theoretical investigations of spectroscopic and magnetic properties of metallic systems in the bulk, as well as in nanostructured materials, have been performed within the density functional theory. The major part of the present work studies the differences between binding energies of electrons tightly bound to the atoms, the so-called core electrons (in contrast with the valence electrons), that is, core-level binding energy shift (CLS).

By comparison between corresponding elemental core-levels for atoms situated in different chemical environments we obtain fundamental understanding of bonding properties of materials. The method of choice was the complete screening picture, which includes initial and final state effects on the same footing. The usefulness of CLS stems from that it is sensitive to differences in the chemical environment of an atom, which can be affected on one hand by the global composition of e.g. disordered materials, surfaces and interfaces, and on the other hand by the very local environment around an atom. Here CLSs have been obtained for both components in the fcc random alloys AgPd, CuPd, CuNi, CuPt, CuAu, PdAu, NiPd and NiPt. Moreover the model was extended to the Auger kinetic energy shift for the LMM Auger transition in AgPd alloys. Studies were also applied to the near surface and interface regions of PdMn nano structures on Pd(100), thin CuPd and AgPd films on inert Ru(0001), and at interfaces. The disorder broadening on CLS due to local environment effects was calculated in selected alloys.

A part of the thesis concern investigations related to the magnetic ordering in Invar alloys, including the influence of local environment effects. A study was made for the dependence of effective exchange parameter on the electron concentration, volume and local chemical composition.

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Maggi, Luca [Verfasser], Paolo [Akademischer Betreuer] Carloni, and Benjamin [Akademischer Betreuer] Stamm. "How vibrational energy exchange study in proteins can shed the light on important biological functions / Luca Maggi ; Paolo Carloni, Benjamin Stamm." Aachen : Universitätsbibliothek der RWTH Aachen, 2020. http://d-nb.info/1240689373/34.

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Colson, Tobias A., and tobiascolson@gmail com. "Large Angle Plasmon Scattering in Metals and Ceramics." RMIT University. Applied Sciences, 2007. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20090212.143048.

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This investigation is primarily concerned with the low loss, or plasmon region of an electron energy loss spectrum. Specifically, why these spectra have the shape and form that they do; what the significance of the material is in determining the shape and form of these spectra; what can be done with plasmon excited electrons; and how all of this fits in with the current theory of plasmon excitation. In particular, the concept of plasmon scattering being an energy transfer process of a coupled wave in the material is explored. This gives rise to slightly different explanations of the plasmon scattering process to the status quo. Multiple scattering is typically pictured as a combination of separate and independent, elastic and inelastic scattering events interactively contributing to a final exit wave function. However, this investigation explores the idea of the elastic and inelastic components being a coupled event, and what the consequences of this idea are from a conceptual point of view. The energy transfer process itself, does not deviate from a virtual particle exchange description that is consistent with the standard model. However, the two significant points made throughout the chapters are one: that the elastic and inelastic scattering events are coupled rather than separate, and two: that each succussive higher order scattering event in multiple scattering scenarios, are dependant and connecte d rather than independent.

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Rvachev, Marat. "Study of the Quasielastic {sup 3}He(e,e{prime}p) Reaction at Q{sup 2}=1.5 (GeV/c){sup 2} up to Missing Momenta of 1 GeV/c." Washington, D.C : Oak Ridge, Tenn. : United States. Dept. of Energy. Office of Energy Research ; distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy, 2003. http://www.osti.gov/servlets/purl/824894-w3sMWi/native/.

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Thesis (Ph.D.); Submitted to Massachusetts Inst. of Tech., Cambridge, MA (US); 1 Sep 2003.
Published through the Information Bridge: DOE Scientific and Technical Information. "JLAB-PHY-03-167" "DOE/ER/40150-2745" Marat Rvachev. 09/01/2003. Report is also available in paper and microfiche from NTIS.

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Santo, Luca. "AA-CAES physical modelling: integration of a 1D TES code and plant performance analysis." Thesis, Uppsala universitet, Tillämpad kärnfysik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-360448.

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The focus of this thesis work was the development of an approachto couple a previosly existing Thermal Energy Storage (TES) modelwritten in C++ with a Simulink/Simscape plant model to simulate anAdvanced Adiabatic Compressed Air Energy Storage (AA-CAES) plant.After the creation and validation of such tool, the complete modelwas used to run simulations, with the aim of assessing the AA-CAESplant's performance under multiple patterns of charge anddischarge.Most of the works found in the literature only provide values ofstorage efficiency obtained from analytical approaches, whilethose that use simulation tools provide average values ofefficiencies when the plant is performing a series of identicalcycles of charge and discharge. During this thesis project,instead, simulations were performed for consecutive irregularcycles determined as the plant response to the electric grid powerrequest. The average efficiency values obtained provide thereforea better representation of how the plant would perform in realapplications.The results show that, under the assumptions made, the AA-CAESplant's overall storage efficiency is influenced very weakly byalterations of the charge-discharge patterns, and that goodperformances can be expected not only for identical chargedischargeconsucutive cycles, but for any pattern that observesthe cavern pressure limits, as long as the thermal energy storageis sized wisely.In addition, a sensitivity analysis was performed in order toassess the influence of turbomachinery efficiency on overallstorage efficiency, for a specified plant layout. The results showthat the turbine efficiency is the most affecting parameter to theplant's performance, while the impact of the main compressors'sinefficiency is mitigated by the thermal recovery that takes placein the TES.The present work confirms that AA-CAES is a promising technologyand that storage efficiencies above 70% can be achieved even inrealistic production scenarios.Finally, future steps for more accurate simulations of plants'performances and more detailed energy production scenarios areproposed.MSc ET 18007Examinator: Joakim WidénÄmnesgranskare: Ane HåkanssonHandledare:

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Penttilä, Jens. "Temperaturzoner för lagring av värmeenergi i cirkulärt borrhålsfält." Thesis, KTH, Energiteknik, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-128951.

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The thermal response of a borehole field is often described by non‐dimensional response factors called gfunctions.The g‐function was firstly generated as a numerical solution based on SBM (Superposition BoreholeModel). An analytical approach, the FLS (Finite Line Source), is also accepted for generating the g‐function. In thiswork the potential to numerically produce g‐functions is studied for circular borehole fields using the commercialsoftware COMSOL. The numerical method is flexible and allows the generation of g‐functions for any boreholefield geometry. The approach is partially validated by comparing the solution for a square borehole field containing36 boreholes (6x6) with g‐functions generated with the FLS approach and with the program EED (Earth EnergyDesigner). The latter is based on Eskilsons SBM, one of the first documents where the concept of g‐functions wasintroduced. Once the approach is validated, the square COMSOL model is compared with a circular geometryborehole field developed by the same method, consisting of 3 concentric rings having 6, 12, and 18 boreholes.Finally the influence on the circular geometry g‐function is studied when connecting the boreholes in radial zoneswith different thermal loads.
Den termiska responsen för ett borrhålsfält beskrivs ofta med den dimensionslösa responsfunktionen kallad gfunktion.Responsfunktionen togs först fram som en numerisk lösning med SBM (Superposition Borehole Model).En analytisk metod, FLS (Finite Line Source) är också accepterad för framtagandet av g‐funktioner. I det här arbetetundersöks förutsättningarna att numeriskt ta fram g‐funktioner för cirkulära borrhålsfält genom att använda detkommersiella simuleringsprogrammet COMSOL Multiphysics. Den numeriska metoden är flexibel och kananvändas för alla typer av borrhålsgeometrier. Metoden att använda COMSOL valideras delvis genom att jämföraresultatet för ett kvadratiskt borrhålsfält innehållande 36 borrhål (6x6) med lösningar framtagna med FLS och meddimensioneringsprogrammet EED (Earth Energy Designer). Det senare har sin grund i Eskilsons SBM, ett av deförsta arbeten där begreppet g‐funktion introducerades. När metoden att använda COMSOL verifierats, jämförsden kvadratiska borrhålsmodellen med en cirkulär borrhålskonfiguration, upprättad med samma metod,innehållande 3 koncentriska ringar om vardera 6, 12, 18 borrhål. Slutligen undersöks hur den termiska responsenpåverkas då borrhålen i ett cirkulärt borrhålsfält kopplas samman och grupperas i radiella zoner med olika termiskalaster.
SEEC Scandinavian Energy Efficiency Co.

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Tizaoui, Abdelkhalek. "Etude théorique, numérique et expérimentale de l'échange de chaleur entre un fluide et le sol par un échangeur bitubulaire vertical." Valenciennes, 1989. https://ged.uphf.fr/nuxeo/site/esupversions/4e75693b-4fbb-4e3f-9f3d-b412562fb545.

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La thèse est consacrée à l’étude de l’échange de chaleur entre un fluide et un milieu solide tel que le sol par l’intermédiaire d’un échangeur bitubulaire vertical. Un modèle mathématique du comportement du système a été élaboré. Pour résoudre l’ensemble des équations, un algorithme de calcul numérique, basé sur l’utilisation des fonctions de Green afin de réduire le problème tridimensionnel à un problème bidimensionnel, a été mis au point. L’application du théorème de Duhamel a permis d’introduire la notion de réponse caractéristique de ce type d’échangeur. En vue de valider le modèle mathématique et numérique, une expérience a été réalisée en laboratoire. Les résultats des tests effectués avec des conditions aux limites différentes confirment avec une très bonne approximation les résultats théoriques. Ce modèle peut être alors utilisé comme un outil intéressant pour concevoir des échangeurs à puits multiples efficaces contribuant ainsi à l’élaboration de chaînes énergétiques rentables.

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"New approaches for incorporating the exact exchange energy density into density functional approximations." Thesis, 2009. http://hdl.handle.net/1911/61758.

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In the last ten years, hybrid density functional approximations have become the most widely used method in modern quantum chemistry. Hybrid functionals combine the semi-local exchange-correlation and a fraction of the exact-exchange energy. The most common are global hybrid functionals, with a constant fraction of the exact exchange determined emprirically. Recently, two complementary strategies have been proposed to improve the performance of hybrid functionals. In range-separated hybrid functionals, the fraction of exact exchange depends on the interelectronic distance. In local hybrid functionals, the fraction of exact exchange is position-dependent. In this work, we propose two approaches that combine range-separated and local hybrid functionals together, providing a promising route to more accurate results. Most previous implementations of range-separated hybrid functionals use a universal, system-independent screening parameter, fitted to experimental data. However, the screening parameter proves to depend strongly on the choice of the training set. Moreover, such functionals violate the exact high-density limit. In this work, we argue that the separation between short-range (SR) and long-range (LR) interactions should depend on the local density. We propose an approximation that uses a position-dependent screening function o( r) defining a local range separation (LRS) for mixing exact (HF-type) and LSDA exchange. This method adds a substantial flexibility to describe diverse chemical compounds. Moreover, the new model satisfies a high-density limit better than the approximation with fixed screening parameter. We have also developed an alternative strategy to improve the range-separated functionals by combining them together with local hybrid functionals. We consider two limiting cases: screened local hybrids with short-range exact exchange, and long-range corrected hybrids with long-range exact exchange. The former approach can treat metals and narrow-gap semiconductors much more efficiently than standard local hybrids do. The latter method provides the correct asymptotic behavior, which is important for the treatment of charge transfer and Rydberg excitations in finite systems.

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Wang, Rodrigo. "Systematic construction of models for the exchange hole of density functional theory." Thèse, 2015. http://hdl.handle.net/1866/13627.

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Sanghi, Shilpi. "Ion mobility studies of functional polymeric materials for fuel cells and lithium ion batteries." 2011. https://scholarworks.umass.edu/dissertations/AAI3482662.

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The research presented in this thesis focuses on developing new functional polymeric materials that can conduct ions, H+, or OH - or Li+. The motivation behind this work was to understand the similarities and/or differences in the structure property relationships between polymer membranes and the conductivity of H+ and OH - ions, and between polymer membranes and the anhydrous conductivity of H+ and Li+ ions. This understanding is critical to developing durable polymer membranes with high H+, OH - and Li+ ion conductivity for proton exchange membrane fuel cells (PEMFCs), alkaline anion exchange membrane fuel cells (AAEMFCs) and lithium ion batteries respectively. Chapter 1 describes the basic functioning of PEMFCs, AAEMFCs and lithium ion batteries, the challenges associated with each research topic, and the fundamental mechanisms of ion transport. The proton conducting properties of poly(4-vinyl-1H-1,2,3-triazole) were investigated on a macroscopic scale by impedance spectroscopy and microscopic scale by solid state MAS NMR. It was found that proton conductivity is independent of molecular weight of the polymer, but influenced by orders of magnitude by the presence of residual dimethylformamide. To improve the mechanical properties of otherwise liquid-like 1H-1,2,3-triazole functionalized polysiloxane homopolymers, hybrid inorganic-organic proton exchange membranes (PEMs) containing 1H-1,2,3-triazole grafted alkoxy silanes were synthesized, using sol-gel chemistry. This method enabled self-supporting membranes having proton conductivity comparable to uncrosslinked homopolymers. One of the biggest challenges with AEMs for use in AAEMFCs is finding a cationic polyelectrolyte that is chemically stable at elevated temperatures in high pH environment. Novel triazolium ionic salts were developed, having greater chemical stability under alkaline conditions compared to existing imidazolium ionic salts. However, the chemical stability of triazolium cations was not sufficient for AAEMFC applications. Excellent chemical stability of (C5H5)2Co+ in 2 M NaOH at 80°C over 30 days was demonstrated and polymerizable vinyl functionalized cobaltocenium monomers were synthesized. This work paves the way for future development of AEMs containing cobaltocenium moieties to facilitate hydroxide ion transport. Polymers containing covalently attached cyclic carbonates were synthesized and doped with lithium triflate and their lithium ion conductivities were investigated. The findings highlight the importance of high charge carrier density and flexibility of the polymer matrix to achieve high lithium ion conductivity. These results are similar to the key factors influencing anhydrous proton transport.

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Wagner, Christopher E. "Exchange energy and potential using the Laplacian of the density." 2012. http://liblink.bsu.edu/uhtbin/catkey/1671227.

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The challenge of density functional theory is the useful approximation of the exchange - correlation energy. This energy can be approximated with the local electron density and the gradient of the density. Many different generalized gradient approximations (GGA) have been made recently and there is controversy over the best overall functional. Recent Monte Carlo simulations give evidence that the Laplacian of the density might be a better starting place than the gradient to correct the local density approximation. We have tested several Laplacian based GGA models for exchange for small atoms. We use known constraints on the exchange energy used in current GGA’s. In many models unphysical oscillations occur in the potential when using the Laplacian, and understanding and eliminating them is part of the focus of this research. We also find that mixing gradient and Laplacian seems to give a better result than only using one or the other.
Department of Physics and Astronomy

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Haldar, S., A. Ghorai, and D. Sen. "Vacancy formation energy of simple metals using reliable model and ab initio pseudopotentials." 2017. https://ul.qucosa.de/id/qucosa%3A31555.

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We present a self-consistent calculation of the mono vacancy formation energy for seven simple metals Li, Na, K, Rb, Cs (all bcc), Al (fcc) and Mg (hcp) using both model and ab initio pseudopotential used in earlier unified studies. The local model pseudopotential calculations show small variations with respect to different exchange-correlation functions and the results are in fair agreement with other similar calculations and the available experimental data. The comparisons show that reliable model (pseudo) potential for simple metals can indeed be obtained for explaining a host of properties. Also, considering the importance of third order term in ab initio calculations, the results of our second order calculation appear fairly reasonable and are comparable with other first principle calculations. The perturbation series being an oscillating one, we hope to improve the calculational results using suitable series convergence acceleration method in the next part of our study.

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Moosavi, Askari Reza. "Experimental and numerical study of a magnetic realization of a Bose-Einstein Condensate in a purely organic spin-1/2 quantum magnet (NIT2Py)." Thèse, 2016. http://hdl.handle.net/1866/20605.

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Dissertations / Theses on the topic 'Exchange energy functional'

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