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Electron-electron interaction and confinement in the integer quantum Hall effectStruck, Alexander. Unknown Date (has links) (PDF)
University, Diss., 2005--Hamburg.
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H- 'H POT. +' e HE- 'H POT. +' confinados via método Hartree-FockCanova, André Luiz Fassone [UNESP] 19 December 2008 (has links) (PDF)
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canova_alf_me_bauru.pdf: 536650 bytes, checksum: a9187371a18d33b935507b73518a7aa2 (MD5) / Esse trabalho tem por objetivo estudar moléculas confinadas via método de Hartree-Fock, de modo a determinar a energia de ligação e do raio de ligação. Estudamos as moléculas de H- 'H POT. +' e HE- 'H POT. +' incluindo os efeitos de blindagem através da modificação da energia de repulsão nuclear. Essa modificação ocorreu pela introdução do fator de blindagem que, ao ser sucessivamente modificado, permitiu um estudo comparativo do comportamento da energia de ligação e do raio de ligação. A relevância desse trabalho para a área de Ciências e Tecnologia de Materiais deve-se ao fato de que a compreensão e o desenvolvimento de materiais e técnicas dependem não somente das espécies químicas, mas também das ligações químicas, pois ambas determinam as características e as propriedades do material. / The main objective of this work was to study the chemical and physical properties, as the bond distance and energy, of confined atoms via Hartree-Fock method. We studied the H- 'H POT. +' e HE- 'H POT. +' molecules introducing the screening effects via modification of the nuclear repulsion energy between atoms allowing thus to understanding the effects in the bond length and energy. The relevance of this work is of prime importance in material science due to many technological applications as molecules confined to surfaces, in liquid helium, neutral plasma and catalysis. All this applications has a common background of knowledge: the influence of the material physical and chemical properties with the distance and energy between the atoms in the chemical composition of the material.
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Finite Element Approach of Electronic Structures / Approche par éléments finis de structures électroniquesFau, Amélie 10 December 2012 (has links)
Grâce à l’amélioration des performances des outils expérimentaux et numériques, la mécanique des matériaux peut explorer des échelles de plus en plus fines. Une meilleure compréhension, voire une prédiction, des phénomènes locaux mis en jeu est alors espérée. Cette thèse s’intéresse à la plus petite échelle impliquée dans le comportement mécanique des matériaux, c.-à-d. les interactions entre noyaux dues au comportement des électrons, et notamment des électrons de valence. L’originalité de ce travail est dans la mise en place des éléments finis comme outil numérique de résolution de ce problème. Cette approche largement utilisée dans le domaine de la mécanique des structures fournit de puissants outils numériques permettant de résoudre le problème électronique. Des modèles de Hartree-Fock et post-Hatree-Fock sont implémentés, et les caractéristiques mécaniques des structures électroniques sont estimées. Ces résultats reposent sur de nombreuses approximations dues aussi bien à la modélisation qu’aux approximations numériques. Des estimateurs d’erreur sont développés pour analyser les résultats. / Since performances of experimental and numerical tools have been largely improved, mechanics of materials can explore smaller and smaller scales. Thus, a better comprehension, or even a prediction, of local phenomena associated with macroscopic deformations are hoped. This dissertation focuses on the smallest scale involved in mechanical behavior of materials, i.e. interactions between nuclei due to electrons behavior and especially to valence electrons. The originality of this work is setting up the finite element method as numerical tool to solve this problem. This approach largely used to solve structural mechanics problems provides powerful numerical tools to tackle electronic structures. The Hartree-Fock and post-Hartree-Fock models are employed, and mechanical properties of electronic structures are estimated. These estimates are based on a set of approximations of both model and numerical origins. Error estimates are proposed to analyze the accuracy of the results.
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Estrutura eletrônica de aglomerados de CO2 com outras moléculas atmosféricas em fase gasosaSouza, Marcílio Bárcry 16 December 2013 (has links)
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Previous issue date: 2013-12-16 / CNPq - Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico / Carbon dioxide (CO2) is one of the most well-known and commonly used molecules
in the scientific world as well as in human society, in general. It is present everywhere from
the interstellar space to the ocean waters. It is present in plants, in human blood and also in
industrial refrigerants. As a greenhouse gas, it absorbs the infrared radiation emitted by the
earth which causes the increase in the atmospheric temperature. So, the study of
intermolecular interactions between the molecules of CO2 with itself and other molecules is
one of the most important and current research topics in molecular physics and quantum
chemistry. Several experimental studies, mainly with spectroscopy of dimers and trimers of
CO2 have been performed in recent decades. However, the number of theoretical works on
clusters of CO2 is much lower compared to experiments. In this regard it is of great
importance to have information on intermolecular interactions and spectroscopic properties of
molecular systems containing CO2. With this motivation, we study intermolecular interactions
with CO2 with itself as well as with water (H2O) , carbonic acid (H2CO3) and methanol
(CH3OH) forming dimers, trimers and tetramers through van der Waals type intermolecular
interactions using the method of Density Functional Theory (DFT) . These clusters can be
represented by (CO2)n + X , where n = 1, 2, 3 and X = H2O, CH3OH, CO2 and H2CO3. Four
different quantum chemical models formed by various combinations of different Gaussian
basis sets and DFT functionals have been used to optimize the molecular geometries and to
calculate the minimum of the potential energy surface of each homogeneous and
heterogeneous CO2 cluster. The models are: B3LYP/6-311++G(d,p), B3LYP/aug-cc-pVDZ,
BHandHLYP/6-311++G (d,p), BHandHLYP/aug-cc-pVDZ. The presence of intermolecular
van der Waals interactions and the formation of hydrogen bonds introduce changes in
structural energetics as well as in electrical and spectroscopic properties. In this work, we
present a systematic analysis of the changes in the structural and energetic properties
(formation of hydrogen bond, binding energies), electric properties (dipole moment, average
polarizability) and spectroscopy of several clusters of CO2 in the gas phase. / Dióxido de carbono (CO2) é uma das moléculas mais conhecidas e utilizadas tanto no
mundo científico quanto na sociedade em geral. Ela está presente em todo lugar desde o
espaço interestelar até nas águas dos mares. Ela está presente nas plantas, no sangue humano e
também nos refrigerantes industrializados. Como um gás de estufa, ela absorve a radiação
infravermelha emitida pela terra que causa o aumento da temperatura terrestre. Por isso, o
assunto de interações intermoleculares entre as moléculas de CO2 com CO2 e também outras
moléculas é um dos mais importantes e atual na pesquisa de física molecular e química
quântica. Vários trabalhos experimentais, principalmente com espectroscopia dos dímeros e
trímeros de CO2 já foram feitos nas últimas décadas. O número de trabalhos teóricos sobre
aglomerados de CO2 é bastante inferior em comparação com experimental. A respeito disso é
de grande importância ter informações sobre interações intermoleculares e propriedades
espectroscópicas de sistemas moléculares contendo CO2. Com esta motivação, estudamos
interações intermoleculares com o próprio CO2, com a água (H2O), ácido carbônico (H2CO3)
e metanol (CH3OH) formando dímeros, trímeros e tetrâmeros estabilizados pelas interações
intermoleculares tipo Van der Waals usando o método da Teoria de Funcional da Densidade
(DFT). Esses aglomerados podem ser representados por ( ) , onde e
H2O, CH3OH, H2CO3 e CO2. Diferentes bases gaussianas e funcionais da DFT formam os
seguintes modelos utilizados para otimizar as geometrias de aglomerados homogênios e
heterogênios de CO2 e cálculo de superfície de potencial mínima: B3LYP/6-311++G(d,p),
B3LYP/aug-cc-pVDZ, BHandHLYP/6-311++G(d,p), BHandHLYP/aug-cc-pVDZ. A
presença de interações intermoleculares de Van der Waals e a formação de ligação de
hidrôgenio mudam as propriedades estruturais, energéticas, elétricas e espectroscópicas. Neste
presente trabalho, apresentamos uma análise sistemática sobre as variações de propriedades
estruturais e energéticas (energia da ligação, ponte de hidrogênio) e elétricas (momento
dipolo, polarizabilidade média) nos vários aglomerados de CO2 em fase gasosa.
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Description relativiste chirale de la matière nucléaire incluant des effets de confinement du nucléon / Chiral relativistic description of nuclear matter including effects of confinement mechanismMassot, Élisabeth 11 September 2009 (has links)
Le but de cette thèse est de construire un modèle décrivant la matière nucléaire symétrique et asymétrique dans une approche relativiste incluant des effets de la chromodynamique quantique, en particulier la symétrie chirale et le confinement. Le système considéré est une assemblée de nucléons en interaction {\it via} l'échange de mésons. L'attraction est assurée par la présence d'un champ scalaire invariant chiral lié aux fluctuations du condensat de quarks. La saturation est obtenue après ajout de la réponse scalaire nucléo- nique liée à la sous-structure en quarks du nucléon. Les paramètres liés au secteur scalaire de l'interaction et au confinement des quarks dans le nucléon sont estimés à partir de données sur réseau. Le reste des paramètres est contraint autant que possible par la phénoménologie hadronique. Le modèle n'est ainsi quasiment pas ajustable, le fait qu'il donne de si bons résultats constitue l'originalité de ce travail de thèse. Dans un premier temps, nous avons choisi de travailler à l'approximation de champ moyen dans le schéma Hartree--Fock. La propagation du champ scalaire dans les termes de Fock conduit à des effets de réarrangement qui permettent de satisfaire le théorème de Hugenhotz--Van Hove. Nous soulignons également le rôle du terme tenseur du $\rho$ dans l'énergie d'asymétrie ainsi que dans la dépendance en isospin de la masse effective de Landau. Enfin, nous donnons l'équation d'état des étoiles à neutrons prédite par ce modèle. Dans un deuxième temps, nous avons décidé d'inclure des effets au-delà du champ moyen en incluant l'énergie de corrélation due aux boucles de pions. Un ingrédient important est l'introduction d'un paramètre de Landau--Migdal contrôlant les interactions à courte portée. L'énergie de corrélation améliore la description des propriétés de la matière nucléaire au niveau du point de saturation. / This work aims at constructing a model for symmetric and asymmetric nuclear matter in a relativistic approach including effects from quantum chromodynamics, in particular chiral symmetry and confinement. We consider an assembly of nucleons interacting via meson exchange. The attraction is due to a chiral invariant scalar field associated with the fluctuations of the chiral condensate. The inclusion of scalar nucleonic effects due to the quark substructure of the nucleon ensures the saturation to occur. The parameters corresponding to the scalar sector of the interaction and to the quarks confinement in the nucleon are obtained from lattice calculations. The rest of the parameters are obtained as much as possible by hadron phenomenology. With such constrained inputs, the results are nevertheless very good: this constitutes the originality of this work. In one part, we chood to work at the mean-field level in the Hartree--Fock scheme. The propagation of the scalar field in the Hartree-Fock terms induce some rearrangement effects which play an essential role in the Hugenhotz--Van hove theorem. We discuss also the role of the tensor part of the $\rho$ interaction in the symmetry energy and the isospin dependance of the Landau effective mass. Then, in the idea to enlarge this work to neutron stars, we give the equation of state predicted by our model. The last step corresponds to the introduction of effects after the mean-field including the correlation energy due to pion loops. An important ingredient is the Landau-Migdal parameter controling short range interactions. The correlation energy enhances the description of the saturation point of nuclear matter
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Density Functional Theory Study of Vibrational Spectra. 8. Assignment of Fundamental Vibrational Modes of 9,10-Anthraquinone and 9,10-Anthraquinone-D<sub>8</sub>Ball, Bryan, Zhou, Xuefeng, Liu, Ruifeng 01 January 1996 (has links)
Density functional theory (using Becke's exchange and Lee-Yang-Parr's correlation functionals (BLYP)) and ab initio Hartree-Fock calculations were carried out in order to investigate the molecular structure and vibrational spectra of 9,10-anthraquinone and its perdeuterated analog. The calculated structural and spectral features are in good agreement with the available experimental results. Most of the BLYP/6-31G* non-CH(D) stretching frequencies are slightly lower than reliable experimental assignments; the mean absolute deviation is about 14 cm-1. On the basis of agreement between calculated and experimental results, assignments of the fundamental vibrational modes were examined and some reassignments were proposed. The calculated results can serve as a guide for a future experimental search for the missing fundamentals of the target molecules.
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Density functional tightbinding studies of Tio2 polymorphsGandamipfa, Mulatedzi January 2020 (has links)
Thesis (Ph. D. (Physics)) -- University of Limpopo, 2020 / Titanium dioxide is among the most abundant materials and it has many of interesting
physical and chemical properties (i.e., low density, high thermal and mechanical
strength, insensitivity to corrosion) that make it a compound of choice for electrodes
materials in energy storage. There are, however, limitations on the theoretical side to
using the main electronic structure theories such as Hartree-Fock (HF) or density functional (DFT) especially for large periodic and molecular systems.
The aim of the theses is to develop a new, widely transferable, self-consistent density
functional tight binding SCC-DFTB data base of TiO2, which could be applied in energy
storage anodes with a large number of atoms. The TiO2, LiTiO2 and NaTiO2 potentials
were derived following the SCC-DFTB parameterization procedure; where the
generalized gradient approximation (GGA) and local density approximation (LDA)
exchange-correlation functional were employed yielding Slater-Koster DFTB
parameters. The results of derived parameters were validated by being compared with
those of the bulk rutile and brookite polymorphs. The structural lattice parameters and
electronic properties, such as the bandgaps were well reproduced. Most mechanical
properties were close to those in literature, except mainly for C33 which tended to be
underestimated due to the choice of exchange-correlation functional. The variation of
the bulk lattice parameter and volume with lithiation and sodiation were predicted and
compared reasonably with those in literature.
The newly derived DFTB parameters were further used to calculate bulk properties of
the anatase, which is chemically more stable than other polymorphs. Generally, the
accuracy of the lattice structural, electronic and mechanical properties of the bulk
anantase were consistent with those of the rutile and brookite polymorphs.
Furthermore, nanostructures consisting of a large number of atoms, which extend
beyond the normal scope of the conventional DFT calculations, were modelled both
structurally and electronically. Structural variations with lithiation was consistent with
experimental and sodiation tends to enhance volume expansion than lithiation.
Anatase TiO2 and LiTO2 nanotubes of various diameters were generated using
NanoWrap builder within MedeA® software. Its outstanding resistance to expansion
during lithium insertion and larger surface area make the TiO2 nanotube a promising
candidate for rechargeable lithium ion batteries. The outcomes of this study will be
beneficial to future development of TiO2 nanotube and other nanostructures.
Lastly, our DFTB Slater-Koster potentials were applied to recently discovered trigonal
bipyramid (TB), i.e. TiO2 (TB)-I and TiO2 (TB)-II polymorphs, which have enormous 1-
D channels that provide suitable pathways for mobile ion transport. All structural,
electronic properties were consistent with those in literature and all elastic properties
agreed excellently with those that were calculated using DFT methods. Finally, the
bulk structures of the two polymorphs, were lithiated and sodiated versions and
electronic and structural properties were studied, together with the lithiated versions
of associated nanostructures consisting of a large number of atoms. Generally, the
TiO2 (TB)-I structure was found to be mechanically, energetically more stable and
ductile than TiO2 (TB)-II. Hence, it will be beneficial to use TiO2 (TB)-I as an anode
material for sodium ion batteries (SIB), due to its unique ductility and larger 1D
channels. / National Research Fund (NRF), the Department of Science
and Innovation (DSI) Energy Storage Research Development and Innovation initiative
and Materials Modeling Centre
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Spin Trapping Behavior of Some Selected Melatonin Derivatives for Hydroxyl Radicals: A Computational StudyCaesar, Aaron 01 May 2023 (has links) (PDF)
Melatonin (N-acetyl-5-methoxytryptamin, MLT) is a naturally occurring antioxidant which has shown some potential for use as a spin trap. Spin traps react with short lived hydroxyl radicals (HO·) to produce more stable products called spin adducts which may be characterized by electron paramagnetic resonance spectroscopy. However, the relative stability of hydroxyl spin adducts of melatonin derivatives (MLTD) compared to 2-hydroxymelatonin (HO-MLT) has not been examined computationally. Computational studies have been done on four selected MLTD; methylmelatonin (Me-MLT), chloromelatonin (Cl-MLT), cyanomelatonin (CN-MLT), and nitromelatonin (NO2-MLT). Geometry of the structures were optimized at the HF/6-31G(d), cc-pVXZ, (X=D and T) and DFT/B3LYP/6-31G(d), cc-pVDZ and cc-pVTZ levels of theory and extrapolated to the complete basis set limit using cc-pVXZ (X=D, T) basis sets. The lowest relative energy was found to be a mix of results for 2-OH-MLT-Me at HF and 2-OH-MLT-NO2 at DFT.
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A Self-Consistent "Realistic" Pairing Theory with Applications to Two-Nucleon Transfer ReactionsGriffin, Robin Edward 12 1900 (has links)
Scope and Contents: A generalized pairing theory has been developed which diagonalizes matrix elements of the effective nucleon-nucleon interaction in a space of one, two and three-pair excitations from a Skyrme Hartree-Fock solution for deformed rotational nuclei. The "pairing" excitation energy for the configurations of time-reversed pairs of particles is obtained from the Hartree-Fock approximation as opposed to the conventional (BCS) residual interaction point of view. The effects of the finite-range character of the effective nucleon-nucleon interaction are studied in the single-particle structure they induce in the pairing matrix elements. Microscopic form factors for (p,t) and (t, p) reactions between states of the rotational bands built on the K^π=0^+ pairing solution band-head states are constructed in the cylindrical Harmonic-Oscillator basis in which the Hartree-Fock solution is expanded. These form factors are used in DWBA calculations for the differential cross-sections. Preliminary calculations for (p,t) and (t,p) transitions between states in 172Yb and 174Yb were performed. The calculations emphasize the effects of structure in the pairing matrix elements, and the necessity for a self-consistent calculation of the diagonal pairing matrix elements sing the Hartree-Fock equations. / Thesis / Doctor of Philosophy (PhD)
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Anwendung von Tensorapproximationen auf die Full Configuration Interaction MethodeBöhm, Karl-Heinz 12 September 2016 (has links) (PDF)
In dieser Arbeit werden verschiedene Ansätze untersucht, um Tensorzerlegungsmethoden auf die Full-Configuration-Interaction-Methode (FCI) anzuwenden. Das Ziel dieser Ansätze ist es, zuverlässig konvergierende Algorithmen zu erstellen, welche es erlauben, die Wellenfunktion effizient im Canonical-Product-Tensorformat (CP) zu approximieren. Hierzu werden drei Ansätze vorgestellt, um die FCI-Wellenfunktion zu repräsentieren und darauf basierend die benötigten Koeffizienten zu bestimmen.
Der erste Ansatz beruht auf einer Entwicklung der Wellenfunktion als Linearkombination von Slaterdeterminanten, bei welcher in einer Hierarchie ausgehend von der Hartree-Fock-Slaterdeterminante sukzessive besetzte Orbitale durch virtuelle Orbitale ersetzt werden. Unter Nutzung von Tensorrepräsentationen im CP wird ein lineares Gleichungssystem gelöst, um die FCI-Koeffizienten zu bestimmen.
Im darauf folgenden Ansatz, welcher an Direct-CI angelehnt ist, werden Tensorrepräsentationen der Hamiltonmatrix und des Koeffizientenvektors aufgestellt, welche zur Lösung des FCI-Eigenwertproblems erforderlich sind. Hier wird ein Algorithmus vorgestellt, mit welchem das Eigenwertproblem im CP gelöst wird.
In einem weiteren Ansatz wird die Repräsentation der Hamiltonmatrix und des Koeffizientenvektors im Fockraum formuliert. Dieser Ansatz erlaubt die Lösung des FCI-Eigenwertproblems mit Hilfe verschiedener Algorithmen. Diese orientieren sich an den Rayleighquotienteniterationen oder dem Davidsonalgorithmus, wobei für den ersten Algorithmus eine zweite Version entwickelt wurde, wo die Rangreduktion teilweise durch Projektionen ersetzt wurde. Für den Davidsonalgorithmus ist ein breiteres Spektrum von Molekülen behandelbar und somit können erste Untersuchungen zur Skalierung und zu den zu erwartenden Fehlern vorgestellt werden.
Schließlich wird ein Ausblick auf mögliche Weiterentwicklungen gegeben, welche eine effizientere Berechnung ermöglichen und somit FCI im CP auch für größere Moleküle zugänglich macht. / In this thesis, various approaches are investigated to apply tensor decomposition methods to the Full Configuration Interaction method (FCI). The aim of these approaches is the development of algorithms, which converge reliably and which permit to approximate the wave function efficiently in the Canonical Product format (CP). Three approaches are introduced to represent the FCI wave function and to obtain the corresponding coefficients.
The first approach ist based on an expansion of the wave function as a linear combination of slater determinants. In this hierarchical expansion, starting from the Hartree Fock slater determinant, the occupied orbitals are substituted by virtual orbitals. Using tensor representations in the CP, a linear system of equations is solved to obtain the FCI coefficients.
In a further approach, tensor representations of the Hamiltonian matrix and the coefficient vectors are set up, which are required to solve the FCI eigenvalue problem. The tensor contractions and an algorithm to solve the eigenvalue problem in the CP are explained her in detail.
In the next approach, tensor representations of the Hamiltonian matrix and the coefficient vector are constructed in the Fock space. This approach allows the application of various algorithms. They are based on the Rayleight Quotient Algorithm and the Davidson algorithm and for the first one, there exists a second version, where the rank reduction algorithm is replaced by projections. The Davidson algorithm allows to treat a broader spectrum of molecules. First investigations regarding the scaling behaviour and the expectable errors can be shown for this approach. Finally, an outlook on the further development is given, that allows for more efficient calculations and makes FCI in the CP accessible for larger molecules.
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