A formação de camadas de cargas elétricas na superfície de Hélio liquido e em filmes de H´leio sobre um substrato está bem estabelecida tanto teórica quanto experimentalmente. Não existia, porém, até o presente, um cálculo auto-consistente para essas camadas de cargas, pois no regime de baixas densidades eletrônicas, estes sistemas podem ser tratados como o problema de 1-elétron. Em nosso trabalho incluímos os efeitos de muitos corpos usando a aproximação de Hartree-Fock e, via cálculos auto-consistentes, mostramos que estes efeitos tornam-se relevantes para densidades a partir de 108 e/cm2 para elétrons sobre Hélio e 103 e/ cm2 para elétrons sobre filme de Hélio. Calculamos também a mobilidade desses elétrons, em superfície de Hélio, incluindo dois mecanismos diferentes de espalhamento; as interações elétron-ripplons e elétrons-átomos de vapor. Usando nossos cálculos auto-consistentes obtivemos resultados que melhores concordam com dados experimentais para a mobilidade, em regimes de altas densidades eletrônicas / The formation of electric charged layers outside liquid Helium and outside films are well understood experimentally as well as theoretically. But, until today, there was not a self-consistent calculation for these electronic layers because, at low densities, these system can be treated as a one-electron problem. In this work we have included the many-body effects using the Hartree-Fock approximations and, via self-consistent calculations, we pointed out that these effects are relevants for densities above 108 e/cm2 for liquid Helium and 103 e/ cm2 for Helium films. We also have calculated the electronic mobility due to different scattering mechanisms: electron-ripplon and electron-vapour interactions. Using our self-consistents calculations we have obtained results that fit very well the experimental data, at high densities

L’augmentation de la puissance électrique des composants électroniques pose le problème de la dissipation de la chaleur générée. Les boîtiers électriques doivent permettre la dissipation de cette chaleur en conservant une isolation électrique. La solution retenue pour évacuer la chaleur par transfert thermique consiste en matériaux composites dont les renforts par leur structuration vont améliorer la conductivité thermique. Des composites à matrice polymère ont été choisis pour leur aptitude de mise en forme. La conductivité thermique et l’isolation électrique sont assurées par des charges céramiques. Les méthodes d’homogénéisation donnent des pistes d’amélioration du comportement de composites en fonction des propriétés de leurs constituants, de leur géométrie et de leur distribution. Elles fournissent ainsi une formulation optimisée de matériaux répondant à certaines caractéristiques issues de cahiers des charges émanant du partenaire industriel (Institut de Soudure). La conductivité thermique attendue des composites impose une forte fraction volumique de charges pour compenser le caractère isolant de la matrice polymère. Des méthodes d’homogénéisation ont été développées pour prédire la conductivité thermique effective pour de forts taux de charges (supérieur à 20%) et des contrastes élevés de conductivité thermique. La présence d’une interphase provenant d’incompatibilités fortes entre les composants doit également être modélisée / The increase of electronic components in the integrated circuits and the required electrical power set the question of the dissipation of the heat generated. The electrical box must favor the heat dissipation while maintaining electrical insulation. The solution chosen to transfer the heat is to develop composite materials whose reinforcements by their structure will improve the thermal conductivity. Polymer-based composite materials were chosen for their building ability. Thermal conductivity and electrical insulation are insured by ceramic reinforcements. The homogenization methods allow to improve the composites’ design according to the properties of their constituents, their geometry and their distribution. They thus provide an optimized formulation of materials satisfying the characteristics emanating from the industrial partner (‘Institut de Soudure’). The expected thermal conductivity of the composites imposes a high volume fraction of reinforcements to counterbalance the insulating polymer matrix. Homogenization methods have been developed to provide predictions of effective thermal conductivity for high (greater than 20%) reinforcement rates and high thermal conductivity contrasts. The presence of an interphase resulting from strong physico-chemical incompatibilities between the components must also be modeled

<p>This thesis is divided into two parts. In the first part we study thermodynamics of the two-dimensional Heisenberg ferromagnet with dipolar interaction. This interaction breaks the conditions of the Mermin-Wagner theorem, resulting in a finite transition temperature. Our calculations are done within the framework of the self-consistent spin-wave theory (SSWT), which is modified in order to include the dipolar interaction. Both quantum and classical versions of the Heisenberg model are considered.</p><p>The second part of the thesis investigates the chemical bonding in solids from the first principles calculations. A new chemical bonding indicator called balanced crystal orbital overlap population (BCOOP) is developed. BCOOP is less basis set dependent than the earlier indicators and it can be used with full-potential density-functional theory (DFT) codes. We apply BCOOP formalism to the chemical bonding in the high-T_c superconductor MgB2 and the theoretically predicted MAX phase Nb3SiC2. We also study how the chemical bonding results in a repulsive hydrogen–hydrogen interaction in metal hydrides. The role of this interaction in the structural phase transition in Ti3SnHx is investigated.</p>

This thesis is divided into two parts. In the first part we study thermodynamics of the two-dimensional Heisenberg ferromagnet with dipolar interaction. This interaction breaks the conditions of the Mermin-Wagner theorem, resulting in a finite transition temperature. Our calculations are done within the framework of the self-consistent spin-wave theory (SSWT), which is modified in order to include the dipolar interaction. Both quantum and classical versions of the Heisenberg model are considered. The second part of the thesis investigates the chemical bonding in solids from the first principles calculations. A new chemical bonding indicator called balanced crystal orbital overlap population (BCOOP) is developed. BCOOP is less basis set dependent than the earlier indicators and it can be used with full-potential density-functional theory (DFT) codes. We apply BCOOP formalism to the chemical bonding in the high-T_c superconductor MgB2 and the theoretically predicted MAX phase Nb3SiC2. We also study how the chemical bonding results in a repulsive hydrogen–hydrogen interaction in metal hydrides. The role of this interaction in the structural phase transition in Ti3SnHx is investigated.

L’auto-assemblage de macromolécules amphiphiles dans des solutions aqueuses est un mécanisme important sous-jacent à de nombreux processus présents dans les organismes vivants. La formation spontanée de structures auto-organisées de phospholipides et de biomacromolécules se produit en raison d'un équilibre délicat entre les forces d'attraction et de répulsion. Ces forces comprennent l'attraction hydrophobe, la liaison hydrogène, les forces de coordination des métaux et la répulsion stérique ou électrostatique. En outre, l'auto-assemblage de molécules amphiphiles synthétiques est largement utilisé dans divers domaines technologiques. Un exemple frappant est celui des surfactants de faible poids moléculaire qui peuvent modifier de manière significative les propriétés des systèmes. Les autres domaines importants dans lesquels les tensioactifs et les macromolécules amphiphiles sont activement utilisés sont la cosmétologie et l'hygiène. Cependant, l'utilisation de structures auto-organisatrices de macromolécules amphiphiles nécessite une étude approfondie et soulève quelques questions pour les chercheurs concernant leur structure, leur comportement sous l'influence de facteurs externes et leur stabilité. L'objectif principal de la thèse était de développer une théorie de champ analytique auto-cohérente de l'auto-organisation dans des solutions de copolymères de déblocage non ioniques linéaires dendritiques et dendritiques doubles dans des solvants sélectifs. Cette théorie nous permet de prédire comment la dendronisation d'un ou des deux blocs affecte les propriétés structurelles et thermodynamiques d'assemblages auto-organisés formés par des copolymères. Il a été démontré que la dendronisation des corona bloc permet d’obtenir les micelles stables de taille relativement petite, mais avec de nombreux groupes terminaux. Cette dernière caractéristique est particulièrement intéressante dans le contexte de la liberation contrôlée, puisque les groupes terminaux exposés à l'environnement peuvent être facilement fonctionnalisés par des groupes de ligands pouvant être ciblés. Ces deux caractéristiques peuvent être obtenues simultanément car la dendronisation des corona bloc réduit le nombre d'agrégation à l'équilibre et les dimensions globales des micelles par rapport aux micelles formées par des molécules de copolymères diblocs linéaires homologues tout en conservant un grand nombre de groupes terminaux par micelle. La dendronisation du bloc insoluble peut être utilisée pour augmenter le nombre d'unités monomères terminales dans le core. Nous avons également démontré que la dendronisation des blocs solubles favorise la formation de micelles sphériques, alors que les gammes de stabilité thermodynamique des micelles cylindriques et des dendrimersomes sont déplacées vers un degré plus élevé de polymérisation des séquences insolubles. Au contraire, la dendronisation du bloc insoluble a l'effet inverse et conduit à un élargissement des gammes de stabilité des polymeres et des micelles cylindriques.Nous avons étudié les effets de l'extensibilité finie dans les brosses polyélectrolytes à chaîne linéaire et à dendron contenant des groupes ioniques. Nous avons développé la théorie analytique des brosses polyélectrolytiques dans l'approximation de Poisson-Boltzmann qui explique explicitement l'extensibilité finie des chaînes de polyélectrolytes formant des brosses. Il a été montré que pour la même série de paramètres de la brosse, la théorie basée sur l’élasticité non linéaire des polyions prédit une épaisseur de la brosse plus faible et une plus grande amplitude du saut de la densité du polymère au bord du pinceau. Les connaissances obtenues fourniront une base rationnelle pour la conception moléculaire de nouveaux copolymères à blocs complexes sur le plan architectural, y compris ceux destinés à des applications médicales. / An important mechanism underlying many processes occurring in living organisms is self-assembly of amphiphilic (macro)molecules in aqueous solutions. Spontaneous formation of self-organized structures of phospholipids and biomacromolecules occurs because of a delicate balance between attraction and repulsion forces. Such forces include hydrophobic attraction, hydrogen bonding, metal coordination forces and steric or electrostatic repulsion.In addition, self-assembly of synthetic amphiphilic molecules is widely used in various technical fields. A striking example are low molecular weight surfactants (small amphiphilic molecules) that can significantly change the properties of systems. Other important areas in which surfactants and amphiphilic macromolecules are actively used are cosmetology and hygiene. However, the use of self-organizing structures of amphiphilic macromolecules requires detailed study and raises a few questions for researchers regarding their structure, behavior under the influence of external factors and their stability.The main goal of the present work was development of the theory of self-assembly of diblock copolymers where one or both of blocks (soluble or/and insoluble) exhibit dendritic branching and established relations between degree of branching of the block(s) and structural properties (size, shape, aggregation number) of the self-assembled aggregates.The major focus of the thesis was on developing an analytical self-consistent field theory of self-organization in solutions of non-ionic linear-dendritic and double-dendritic deblock copolymers in selective solvents. This theory enables us to predict how dendronization of one or both blocks affects structural and thermodynamic properties of self-organized assemblies formed by copolymers. It was demonstrated that dendronisation of the corona blocks allows obtaining the stable micelles of relatively small size, but with many terminal groups.The latter feature is most attractive in the context of controlled delivery, since the exposed to the environment terminal groups can be readily functionalized by targetable ligand groups. Both these features can simultaneously be achieved because dendronization of the corona blocks reduces the equilibrium aggregation number and overall dimensions of micelles compared to micelles formed by homologous linear-linear diblock copolymer molecules while keeping large number of terminal groups per micelle. Dendronization of the insoluble block may be used for increasing of the number of terminal monomer units in the core. Such terminal groups can be further functionalized to be able to interact with active drugs, thereby increasing the loading capacity of the micelle.We have also demonstrated that dendronization of the soluble blocks favors formation of spherical micelles, whereas the ranges of thermodynamic stability of cylindrical wormlike micelles and dendrimersomes are shifted to larger degree of polymerisation of the insoluble blocks. On the contrary, dendronization of the insoluble block has the opposite effect and leads to widening of the stability ranges of polymersomes and cylindrical micelles.We investigated effects of finite extensibility (non-linear elasticity) in linear chain and dendron polyelectrolyte brushes containing ionic groups. We developed the analytical theory of polyelectrolyte brushes within the Poisson-Boltzmann approximation which explicitly accounts for finite extensibility of the brush-forming polyelectrolyte chains. It was shown that for the same set of the brush parameters the theory based on non-linear elasticity of the polyions predicts smaller thickness of the brush and larger magnitude of the jump in polymer density at the edge of the brush.The obtained knowledge will provide a rational background for molecular design of novel architecturally complex block copolymers, including those for medical applications.

A formação de camadas de cargas elétricas na superfície de Hélio liquido e em filmes de H´leio sobre um substrato está bem estabelecida tanto teórica quanto experimentalmente. Não existia, porém, até o presente, um cálculo auto-consistente para essas camadas de cargas, pois no regime de baixas densidades eletrônicas, estes sistemas podem ser tratados como o problema de 1-elétron. Em nosso trabalho incluímos os efeitos de muitos corpos usando a aproximação de Hartree-Fock e, via cálculos auto-consistentes, mostramos que estes efeitos tornam-se relevantes para densidades a partir de 108 e/cm2 para elétrons sobre Hélio e 103 e/ cm2 para elétrons sobre filme de Hélio. Calculamos também a mobilidade desses elétrons, em superfície de Hélio, incluindo dois mecanismos diferentes de espalhamento; as interações elétron-ripplons e elétrons-átomos de vapor. Usando nossos cálculos auto-consistentes obtivemos resultados que melhores concordam com dados experimentais para a mobilidade, em regimes de altas densidades eletrônicas / The formation of electric charged layers outside liquid Helium and outside films are well understood experimentally as well as theoretically. But, until today, there was not a self-consistent calculation for these electronic layers because, at low densities, these system can be treated as a one-electron problem. In this work we have included the many-body effects using the Hartree-Fock approximations and, via self-consistent calculations, we pointed out that these effects are relevants for densities above 108 e/cm2 for liquid Helium and 103 e/ cm2 for Helium films. We also have calculated the electronic mobility due to different scattering mechanisms: electron-ripplon and electron-vapour interactions. Using our self-consistents calculations we have obtained results that fit very well the experimental data, at high densities

Dans cette thèse, deux méthodes de couplage sont proposées pour la simulation multi-échelle des procédés de mise en forme. Dans la première partie, une procédure simplifiée (couplage indirect) est adoptée pour coupler les codes éléments finis (Abaqus et LAM3) au modèle polycristallin avec un schéma de transition autocohérente basée sur le comportement élastoplastique du monocristal écrit dans le formalisme des grandes déformations. Cette procédure simplifiée consiste à lier le modèle polycristallin avec l'analyse EF par l'extraction de l'histoire de l'incrément de déformation et de contrainte macroscopique, obtenue à partir d'une simulation EF préliminaire avec une loi phénoménologique, et à l'utiliser comme trajet de chargement dans le modèle polycristallin. Cette méthode est appliquée pour la simulation multi-échelle du procédé de skin-pass. Le suivi du trajet de chargement extrait dans la demi-épaisseur de la tôle a permis de prédire l'évolution des grandeurs physiques associées au modèle de plasticité en particulier la texture cristallographique, la texture morphologique et l'écrouissage. Dans la seconde partie de cette thèse, un modèle polycristallin élastoplastique du type autocohérent en petites déformations est couplé au code EF Abaqus via la routine utilisateur UMAT. Ce couplage (dit couplage direct) consiste à utiliser la théorie de la plasticité cristalline comme loi de comportement à chaque point d'intégration du maillage EF. Le polycristal est représenté par un ensemble de N monocristaux. Chaque fois que le code EF a besoin d'information sur le comportement mécanique aux points d'intégration de chaque EF, le modèle polycristallin est appelé. Pour valider ce couplage développé, nous avons effectué des cas tests de simulation de trajets rhéologiques. Les résultats issus de ce couplage ont été validés avec des modèles de référence. À la différence des modèles phénoménologiques, ce couplage permet non seulement d'avoir des informations sur le comportement macroscopique de la structure mais aussi d'obtenir des informations sur l'état de la microstructure du matériau. / In this thesis, two coupling methods are proposed for the multiscale simulation of forming processes. In the first part, a simplified procedure (indirect coupling) is adopted to couple the finite element codes (Abaqus and LAM3) with a polycrystalline selfconsistent model based on the large strain elastoplastic behavior of single crystals. This simplified procedure consists in linking the polycrystalline model with the FE analysis by extracting the history of the increment of macroscopic strain and stress, obtained from a preliminary FE simulation with a phenomenological law, and then using it as loading path prescribed to the polycrystalline model. This method is applied to multiscale simulation of skin-pass processes. By following on the loading path extracted at the halfthickness of the sheet, we can predict the evolution of some physical parameters associated with the plasticity model, in particular the crystallographic texture, the morphological texture and hardening. In the second part on this thesis, a small strain version of the elastoplastic polycristalline self-consistent model is coupled to the Abaqus FE code via the user material subroutine UMAT. This coupling (called direct coupling) consists in using crystal plasticity theory as constitutive law at each integration point of the FE mesh. The polycristal is represented by a set of N single crystals. Each time the FE code needs information on the mechanical behavior at the integration points considered, the full polycrystalline constitutive model is called. In order to validate this coupling, simulations of simple mechanical tests have been conducted. The results of this coupling have been validated through comparison with reference models. Unlike phenomenological models, this coupling provides not only information on the overall macroscopic response of the structure, but also important information related to its microstructure

Cette thèse est consacrée à l'étude ab initio des structures électroniques des molécules diatomiques polaires YN, YS, ZrN, et ZrS. Cette étude est motivé par le manque d’informations dans la littérature sur la structure électronique de ces molécules, alors qu’elles ont clairement été identifiées dans le spectre de certaines étoiles. Des calculs théoriques sont ainsi nécessaire puisqu’ils peuvent fournir d'importantes informations quant aux propriétés des états électroniques fondamentaux et excités qui ne sont pas accessibles expérimentalement. Dans ce travail les calculs ab initio ont été effectués par la méthode du champ auto-cohérent de l'espace actif complet (CASSCF), suivie par l'interaction de configuration multiréférence (MRSDCI). La correction de Davidson, notée (MRSDCI+ Q), a ensuite été appliquée pour rendre compte de clusters ou agrégats quadruples non liés. Les calculs ont été effectués selon deux schémas. Dans le premier les effets spin-orbite ont été négligés alors que dans le second les effets spin orbite ont été inclus par la méthode des potentiels de noyau efficaces. Tous les calculs ont été effectués en utilisant le programme de calcul de chimie physique MOLPRO et en tirant parti de l’interface graphique Gabedit. Les courbes d'énergie potentielle ont été construites et des constantes spectroscopiques calculées, ainsi que les moments dipolaires électriques permanent, les champs électriques moléculaires intenses et les structures énergétiques de vibration-rotation. Nous avons détecté dans la molécule ZrS plusieurs niveaux vibrationnels dégénérés ceux-ci peuvent être utilisés pour rechercher les variantes possibles de la constante de structure fine α etdu rapport de masse μ de l’electron par rapport au proton dans trois étoiles de type S, du nomde Rand, les RCas, et χCyg. La comparaison des données expérimentales et théoriques pour la plupart des constantes calculées a montré une bonne précision pour nos prédictions avec une différence relative (en pourcentage) qui varie entre 0,1% et 10%. Ces résultats devraient ainsi mener à des études expérimentales plus poussées pour ces molécules. / This dissertation is dedicated to the ab initio study of the electronic structures of the polardiatomic molecules YN, YS, ZrN, and ZrS. The identification of these molecules in the spectraof stars as well as the lack in literature on the electronic structures of these molecules motivatedthe present study. Theoretical calculations are useful in this respect since they can provideimportant data for the properties of the ground and excited electronic states that are not availablefrom experimental means. In the present work the ab initio calculations were performed at thecomplete active space self-consistent field method (CASSCF) followed by multireference singleand double configuration interaction method (MRSDCI). The Davidson correction noted as(MRSDCI+Q) was then invoked in order to account for unlinked quadruple clusters. Thecalculations were performed on two stages in the first spin orbit effects were neglected while inthe second type of calculations spin orbit effects were included by the method of effective corepotentials. All of the calculations were done by using the computational physical chemistryprogram MOLPRO and by taking advantage of the graphical user interface Gabedit. In thepresent work potential energy curves were constructed and spectroscopic constants computed,along with permanent electric dipole moments, internal molecular electric fields, and vibrationalrotationalenergy structures. We detected in the ZrS molecule several degenerate vibrationalenergy levels which can be used to search for possible variations of the fine structure constant αand the electron to proton mass ratio μ in three S-type stars, named Rand, RCas, and χCyg. Acomparison with experimental and theoretical data for most of the calculated constantsdemonstrated a good accuracy for our predictions giving a percentage relative difference thatranged between 0.1% and 10%. Finally, we expect that the results of the present work shouldinvoke further experimental investigations for these molecules.

Thermal oxidation of silicon belongs to the most decisive steps in microelectronic fabrication because it allows creating electrically insulating areas which enclose electrically conductive devices and device areas, respectively. Deal and Grove developed the first model (DG-model) for the thermal oxidation of silicon describing the oxide thickness versus oxidation time relationship with very good agreement for oxide thicknesses of more than 23 nm. Their approach named as general relationship is the basis of many similar investigations. However, measurement results show that the DG-model does not apply to very thin oxides in the range of a few nm. Additionally, it is inherently not self-consistent. The aim of this paper is to develop a self-consistent model that is based on the continuity equation instead of Fick’s law as the DG-model is. As literature data show, the relationship between silicon oxide thickness and oxidation time is governed—down to oxide thicknesses of just a few nm—by a power-of-time law. Given by the time-independent surface concentration of oxidants at the oxide surface, Fickian diffusion seems to be neglectable for oxidant migration. The oxidant flux has been revealed to be carried by non-Fickian flux processes depending on sites being able to lodge dopants (oxidants), the so-called DOCC-sites, as well as on the dopant jump rate.

This work describes theoretical studies on molecular and electronic structures of lanthanide-based single-molecule magnets focusing on their magnetic properties. In this work, two main problems are covered: the structural ordering of endohedral fullerenes in different supramolecular arrangements, and the magnetic anisotropy of lanthanides in different charge coordinations. The basic methodes used in this work are density functional theory and multiconfigurational self-consistent field.:CHAPTER 1. THEORETICAL FOUNDATIONS OF RARE-EARTH MAGNETISM 12 1.1. Single-molecule magnetism and 4f-elements 14 1.1.1. Electronic structure of 4f-elements 16 1.1.2. LS-coupling scheme 19 1.1.3. Parameterization of the Crystal-Field splitting effect. 20 1.1.4. Zeeman splitting for a free ion 24 1.1.5. Spin Hamiltonian and pseudospin approximation 24 1.1.6. Kramers theorem 25 1.1.7. Weak and strong molecular interactions. 26 1.2. Computational methods in application to Ln-based SMMs 27 1.2.1. Density functional theory (DFT). 28 1.2.2. Multiconfigurational methods in quantum chemistry 33 1.3. Role of molecular structure in single-molecular magnetism 41 1.3.1. Complexes of SMMs with organic molecules 45 1.3.2. SMMs deposited on surfaces 46 CHAPTER 2. STRUCTURAL ORDERING IN COCRYSTALS OF EMFs AND Ni(OEP) 49 2.1. Ordering in endohedral metallofullerenes 49 2.2. Modeling details 51 2.3. Conformer analysis 54 2.4. Electrostatic potential 58 CHAPTER 3. ISOMERISM OF Dy2ScN@C80 DEPOSITED ON SURFACES 61 3.1. Modeling details 62 3.2. Cluster conformation analysis 69 3.3. Charge density analysis 75 CHAPTER 4. Ho|MgO AS A SINGLE-ATOMIC MAGNET. FV-MAGNETISM. 80 4.1. DFT description of Ln|MgO 85 4.2. Ho|MgO system: ab initio calculations 92 4.3. Magnetic properties of lanthanides with FV magnetism 99 4.4. Generalized ligand field and spin Hamiltonians for FV systems. 101 CHAPTER 5. FV-MAGNETISM IN [Ln2+] METALLOCENE COMPLEXES 107 5.1. TbII(CpiPr5)2 DFT-model 108 5.2. FV-interaction in terms of ab initio multiconfigurational approach 113 5.3. Point-charge model 115