The spin polarized first principles pseudofunction (PSF) method with the local spin density approximation (LSDA) has been used to calculate total energies, electronic structures and total and partial densities of states for bulk MnTe in the NiAs structure for both anti-ferromagnetic and ferromagnetic states under the pressure. For the pressure range considered in this study, the anti-ferromagnetic state is thermodynamically more stable than the ferromagnetic state in agreement with experimental observation. For the anti-ferromagnetic state, MnTe has an indirect band gap, which decreases linearly with the increase of the pressure in agreement with experiment. The calculated valence band and conduction band are found to broaden with the increase of the pressure, which can be attributed to the pressure induced shortening of the Mn-Te bond length that enhances hybridization between Mn and Te orbitals.

We use the spin polarized pseudofunction(PSF) method with the local-spin-density approximation (LSDA) to calculate the electronic structures and the total and partial charge densities (TDOS, PDOS) of bulk Ba1-xSrxTiO3 (BSTO) with x = 0, 0.25, 0.5, 0.75, and 1. We find that the calculated direct energy gap Eg bows up as a function of the Sr concentration, which is related to the bowling downward of the Ti-O bond length inferred from the experimental lattice constants. The calculated partial densities of unoccupied O-p derived states (PDOS) agree well with the features observed in the O K-edge XANES spectra of BaTiO3 and SrTiO3. The calculated total densities of valence-band states (TDOS) and the valence-band widths for BaTiO3 and SrTiO3 agree well with the UPS spectra.

Thesis (M.Sc. (Physics)) --University of Limpopo, 2008 / We present first principles structural, electronic and optical properties investigation of PdS, which are carried out using density functional theory under plane wave pseudopotential method within the local density approximation. We used ultrasoft- pseudopotentials to carry out our calculations. Calculated lattice parameters of the system show excellent agreement with the experimental values. The lattice parameters were observed to decrease linearly with increasing pressure. The density of states and optical properties of PdS have been computed under hydrostatic pressure. The actual size of the band gap remains constant with increasing pressure, whilst the peaks just below and above the Fermi energy moves to the left and to the right respectively. We also investigated the effect of compositional variation on our reflectance by calculating the reflectivity of Pd4-xPtxS4 and Pd4-xNixS4. Since we have different positions for the same concentration, we used the heats of formation to determine the most stable structures and these structures were used to study the effect of compositional variation on our reflectance spectrum. We studied the equation of state (EOS), structure under hydrostatic pressure, and deduced the bulk modulus. It is important to study these properties under such extreme conditions of pressure and temperature as they tend to occur below the earth's surface. Investigation of stability and mechanical properties of binary and ternary compounds from PtS to PdS have been carried out, were the presence of the miscibility gap is still uncertain. We investigate stability of these compounds by studying the heats of formation, elasticity and electronic properties. Our results show no miscibility gap but continuum solid solution between these compounds. A shift of the Fermi energy towards the conduction band is observed at a 50% concentration of Pd and Pt. All the information obtained on PdS is intended to assist in fitting interatomic potentials to enable studies of systems with many atoms.

Neste trabalho realizamos o cálculo da estrutura eletrônica de poços quânticos com dopagem seletiva, usando um método k-p com 8 bandas. Utilizamos um processo de bloco-diagonalização para reduzir o Hamiltoniano 8x8 a dois blocos 4x4 a fim de diminuir o esforço computacional. Calculamos o efeito do potencial auto-consistente sobre a massa dos portadores e sobre as densidades de estado. Os resultados obtidos para as energias de excitação de uma partícula estão em pleno acordo com os dados obtidos em experimentos de absorção óptica intra-banda (espalhamento Raman ressonante) / In this work we developed a calculation of the electronic structure of modulation doped quantum wells using a k-p method with 8 bands. We have used a procedure which block-diagonalizes this 8x8 Hamiltonian into two 4x4 blocks to reduce the computacional effort. We have calculated the effect of the self-consistent potential on the effective mass of carriers and on the densities of states. The results obtained for one-particle excitations are in complete agreement with intra-band optic absorptions experiments (resonant Raman scattering)

<p>Cette thèse est consacrée à l'étude des effets isotopiques dans les atomes neutres et ions négatifs. En particulier, nous ciblons notre recherche sur le calcul ab initio des déplacements isotopiques (DI) sur les électroaffinités des éléments des blocs p des deuxième et troisième périodes (B à F et Al à Cl). Ces derniers sont les systèmes les plus susceptibles d'être l'objet d'études expérimentales de haute précision.</p> <p>Le premier chapitre se concentre sur une étude didactique du problème atomique et des effets isotopiques. Nous concluons par une description détaillée des motivations de notre thèse.</p> <p>Le second chapitre présente le modèle Hartree-Fock (HF) et son extension multi-configurationelle (MCHF). Nous y énonçons le théorème de Brillouin et sa généralisation à un ansatz MCHF. Pour ce faire, nous formulons de manière originale le principe d'invariance d'une fonction d'onde CAS (Complete Active Set) par rapport aux rotations d'états d'orbitales. De cette formulation, nous caractérisons la famille des solutions CAS n'interagissant pas avec une fonction d'état de configuration (CSF) particulière et démontrons sa multiplicité. Finalement, nous appliquons notre technique d'analyse à l'étude de modèles concrets et prédisons l'apparition de minima locaux correspondant à chacune de ces solutions GBT. Introduisant le concept de quasi-symétrie de la fonctionnelle d'énergie, nous expliquons l'origine de fortes perturbations du "coeur" atomique dans des modèles particuliers.</p> <p>Les troisième et quatrième chapitres fournissent les outils méthodologiques de base utilisés dans la deuxième partie de notre thèse qui présente des résultats quantitatifs originaux.</p> <p>Le cinquième chapitre traite des DI et structures hyperfines des termes les plus bas de S, S-, Cl, Cl-, Si et Si-.</p> <p>Dans le sixième chapitre, nous rapportons un profond désaccord entre théorie et expérience au sujet de la structure hyperfine de transitions de l'azote dans le infrarouge lointain. Nous montrons que les simulations basées sur nos valeurs de constantes isotopiques sont compatibles avec les spectres enregistrés moyennant une réassignation des raies faibles à des signaux de "cross-overs". Sur cette base, nous déduisons un nouvel ensemble de constantes hyperfines pour les états considérés, en bon accord avec nos valeurs théoriques, en nous basant uniquement sur les données expérimentales.</p> <p>Le septième chapitre est une étude globale des configurations de plus basse énergie du C et C- (i.e. tous les états liés de ce dernier). Par une étude détaillée de nos incertitudes, nous obtenons des estimations très fiables et de grande précision pour un ensemble de propriétés. En particulier, nous présentons les valeurs de structure fine et hyperfine du C-, ainsi que les probabilités de transitions intra-configurationelles fournissant une base solide pour l'étude spectroscopique de ce système.</p> <p>Dans le huitième chapitre, nous étudions la périodicité du déplacement spécifique de masse sur l'électroaffinité dans le Tableau Périodique des Eléments. Nous avançons les contributions dominantes qui interviennent dans cette grandeur et analysons les principales limitations des techniques de calcul actuelles dans ce contexte.</p> <p>Nous présentons nos conclusions générales et les perspectives de notre travail dans le neuvième chapitre.</p> <p>|</p> <p>This thesis is aimed at the study of isotope effects in negative ions and neutral atoms. In particular, we perform ab initio calculations of isotope shift (IS) on the electron affinity of p-block atoms of the second and third periods (B to F and Al to Cl). These atoms are the best candidates for high accuracy experimental studies.</p> <p>The first chapter is a didactical study of the atomic problem and isotope effects. We conclude with a detailed description of the motivations of our thesis.</p> <p>The second chapter presents the Hartree-Fock model (HF) and its multi-configurational extension (MCHF). The Brillouin theorem is formulated together with its generalization to a MCHF ansatz. In order to do that, we propose an original formulation of the invariance principle of a CAS (Complete Active Set) wave function with respect to orbital state rotations. We then characterize the family of CAS solutions that do not interact with a particular configuration state function (CSF), and demonstrate its multiplicity. Finally, we apply our analytical tools to the study of concrete models and predict the appearance of local minima corresponding to each of these GBT solutions. Introducing the concept of quasi-symmetry of the energy functional, we explain the origin of strong perturbations of the atomic "core" in particular models.</p> <p>The third and fourth chapters provide the methodological tools that are used in the second part of our thesis, which present qualitative results.</p> <p>In the fifth chapter, we study the DIs and hyperfine structures of the lowest terms of S, S-, Cl, Cl-, Si and Si-.</p> <p>In the sixth chapter, we report a deep disagreement between theory and experiment concerning the hyperfine structures of far-infrared transitions in nitrogen. We show that simulations based on our set of hyperfine constants are compatible with the recorded spectra if the weak signals are reassigned to "cross-overs". On this basis, we deduce new hyperfine constants for the considered states, in good agreement with the theoretical values, basing our analysis on experimental data only.</p> <p>The seventh chapter is a global study of the lowest configurations of C and C- (i.e. all bound states of the latter). By a detailed study of our uncertainties, we obtain reliable and highly accurate estimations for a series of properties. In particular, we present the fine and hyperfine structures of C-, together with the intra-configurational transition probabilities, which provide a strong basis for spectroscopic investigations of this system.</p> <p>In the eighth chapter, we study the periodicity of the specific mass shift on the electron affinity throughout the Periodic Table. We advance the dominant contributions which contribute to this quantity and analyze the main limitations of the current computation techniques in this context.</p> <p>We present our general conclusions and perspectives of our work in the ninth chapter.</p>

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Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第18982号 / 工博第4024号 / 新制||工||1620 / 31933 / 京都大学大学院工学研究科材料工学専攻 / (主査)教授 田中 功, 教授 酒井 明, 教授 邑瀬 邦明 / 学位規則第4条第1項該当

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.

The electronic spectra of sulfide minerals can be complex, and their features difficult to assign. Often, therefore, they are interpreted using electronic-structure models obtained from quantum-chemical calculations. The aim of this study is to provide such models for the minerals sphalerite, wurtzite, pyrite, marcasite, and chalcopyrite. All are important minerals within a mining context, either as a source for their component metals or as a gangue mineral. They are also semiconductors. Each is the structural archetype for a particular class of semiconductors, and so a knowledge of their electronic structures has wider applicability. / PhD Doctorate