Littérature scientifique sur le sujet « Cristallographie Quantique »
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Thèses sur le sujet "Cristallographie Quantique"
Decarreau, Andrée. « Espaces de Fok, produit tensoriel et fonctions spéciales en mécanique quantique : un problème d’optimisation non convexe en cristallographie : théorie et algorithme ». Poitiers, 1990. http://www.theses.fr/1990POIT2001.
Texte intégralVuković, Vedran. « Calculs électrostatiques rapides dans l'analyse énergétique : Développement de la méthode, applications aux études de cristaux organiques et organométalliques et de complexes protéine/ligand ». Electronic Thesis or Diss., Université de Lorraine, 2021. http://www.theses.fr/2021LORR0163.
Texte intégralOne usually considers the electrostatic nature of atoms to explore intermolecular interactions. The Hansen-Coppens multipolar model is widely used to bring a detailed view of electron distribution on an atomic scale. It is thus a common starting point to investigate chemical behaviour of selected systems, giving access to microscopic insights that elucidate material properties on the large scale.One such property is the electrostatic interaction energy, which tells how strongly two charges attract or repel each other. The multipolar model brings forward a clear picture of charge distributions inside molecules, so a calculation of electrostatic energy based on it provides a better estimate than by using traditional methods (simplifications like point charges). The methods already exist to calculate electrostatic interaction energy, but their weak point is that they take their time to calculate the underlying integrals.The method discussed in this thesis (analytical exact potential / pseudo-multipolar moments, aEP/pMM) replaces the slow numerical integration inherent to the older method with analytical integration. It was integrated in the program Charger. The boost of speed comes from replacing a 3D cubature with a one-dimensional integral, due to favourable mathematical properties of the underlying multipolar model. The improvement in speed goes from 4 to 200 times, and the resulting energies are almost indistinguishable from those obtained by the older method.The goal was also to see how wide one can cast the net of this new Charger approach. It was tested on protein/ligand complexes, organic molecules and metal-organic complexes involving many elements of the first three rows in the periodic table. It was also applied on an organometallic complex containing nickel atoms in its core. In all of these applications, Charger reigned supreme over the old approach in terms of computational time, while guarding exceptional accuracy.The application on the protein/ligand complex pointed to residues which are the major contributors and detractors to ligand binding. It also revealed a possible mutation candidate that could show the predictive power of the Charger approach. The metal-organic complex contained a peculiar contact: Charger helped to characterise it. Charger also unveiled the electrostatic energy of crystal packing for an organic and an organometallic compound. The author hopes that the new aEP/pMM approach will encounter a positive reception and contribute to many an interesting finding across various fields that rely on molecular modeling
Wieduwilt, Erna K. « Quantum mechanics-based methods for the refinement of crystal structures and the analysis of non-covalent interactions ». Electronic Thesis or Diss., Université de Lorraine, 2021. http://www.theses.fr/2021LORR0167.
Texte intégralIn the work presented in this thesis, extremely localized molecular orbitals (ELMOs) were used as electronic LEGO building blocks to accomplish mainly two goals: (i) obtaining more accurate X-ray crystal structures for small and large systems, and (ii) analyzing non-covalent interactions in biomolecules. In fact, ELMOs are molecular orbitals that are strictly localized on small molecular fragments. Due to this strict localization, they may be computed on small molecules, stored in databases and then transferred to larger systems to reconstruct their wavefunctions and electron densities. To this end, we exploited the ELMO libraries, which contain the ELMOs for all the elementary fragments (atoms, bonds and functional groups) of the twenty natural amino acids. In situations where a higher accuracy was needed, we used the QM/ELMO embedding technique, in which the crucial part of the system under exam is treated at a higher quantum mechanical level, while the rest is described using frozen ELMOs. Concerning the first of the goals mentioned above, it is important to note that standard crystallographic refinements are based on the so-called independent atom model (IAM), which approximates the electron density as a sum of spherically averaged atomic densities. However, the element-hydrogen bond lengths resulting from IAM refinements are systematically too short. A method that solves this problem is the Hirshfeld atom refinement (HAR), a technique based on directly computing the electron density for the molecule under exam using quantum mechanical calculations. For small molecules, HAR has been proven to give element-hydrogen bond lengths that are in very good agreement with neutron reference values. However, for large systems, the applicability of the traditional HAR method is limited because the underlying fully QM calculations become computationally too expensive. Therefore, in the work presented in this thesis, the ELMO libraries and the QM/ELMO techniques have been coupled with the HAR method to refine large systems and also to obtain more accurate structures of small molecules. Furthermore, the necessity of using post-HF methods for HAR has been also evaluated. Concerning the second goal addressed in this dissertation, a similar problem as the one met in X-ray crystallography also arises in the analysis of non-covalent interactions. In fact, also the non-covalent interaction (NCI) and independent gradient model (IGM) techniques, which are commonly applied in analyses of non-covalent interactions, crucially depend on the computation of the electron density. Therefore, to analyze non-covalent interactions in large systems, both techniques had to resort to promolecular electron densities, which are the same densities used in the IAM. However, also in the cases of NCI and IGM analyses, these densities provide biased results. To overcome this drawback, we have coupled both methods with the ELMO libraries, giving rise to the NCI-ELMO and IGM-ELMO techniques, which were then applied to identify, classify and approximately quantify non-covalent interactions in polypeptides and proteins
Gasca, Petrica. « Zirconium – modélisation ab initio de la diffusion des défauts ponctuels ». Thesis, Lille 1, 2010. http://www.theses.fr/2010LIL10111/document.
Texte intégralZirconium is the main element of the cladding found in pressurized water reactors, under an alloy form. Under irradiation, the cladding elongate significantly, phenomena attributed to the vacancy dislocation loops growth in the basal planes of the hexagonal compact structure. The understanding of the atomic scale mechanisms originating this process motivated this work. Using the ab initio atomic modeling technique we studied the structure and mobility of point defects in Zirconium. This led us to find four interstitial point defects with formation energies in an interval of 0.11 eV. The migration paths study allowed the discovery of activation energies, used as entry parameters for a kinetic Monte Carlo code. This code was developed for calculating the diffusion coefficient of the interstitial point defect. Our results suggest a migration parallel to the basal plane twice as fast as one parallel to the c direction, with an activation energy of 0.08 eV, independent of the direction. The vacancy diffusion coefficient, estimated with a two-jump model, is also anisotropic, with a faster process in the basal planes than perpendicular to them. Hydrogen influence on the vacancy dislocation loops nucleation was also studied, due to recent experimental observations of cladding growth acceleration in the presence of this element
Shi, Jingming. « Ab initio prediction of crystalline phases and their electronic properties : from ambient to extreme pressures ». Thesis, Lyon, 2017. http://www.theses.fr/2017LYSE1110/document.
Texte intégralIn this thesis we use global structural prediction methods (Particle Swarm Optimization and Minima Hopping Method) and high-throughput techniques to predict crystal structures of different systems under different conditions. We performed structural prediction by using the Crystal structure Analysis by Particle Swarm Optimization (CALYPSO) combined with Density Functional Theory (DFT) that made possible to unveil several stable compounds, so far unknown, on the phase diagrams of Ba-Si systerm and N-H-O system. Afterwards, we performed a high-throughput investigation on ternary compounds of composition ABX2, where A and B are elements of the periodic table up to Bi, and X is a chalcogen (O, S, Se, and Te) by using density functional theory and combining calculations of crystal prototypes with structural prediction (Minima Hopping Method). The following paragraphs summarize the content by chapter of this document. Chapter 1 is a short introduction of this thesis. Chapter 2 consists of the basic theory used in this thesis. Firstly, a short introduction of Density Function Theory (DFT) is presented. Then, we describe some approximate exchange- correlation functions that make DFT practical. Next, we introduce different structural prediction algorithms, especially Particle Swarm Optimization and Minima Hopping Method which we used in this thesis. Finally, we discuss the thermodynamic stablility criteria for a new a new structure. In Chapter 3, we first consider Ba–Si system. Using an unbiased structural search based on a particle-swarm optimization algorithm combined with DFT calculations, we investigate systematically the ground-state phase stability and structural diversity of Ba–Si binaries under high pressure. The phase diagram turns out to be quite intricate, with several compositions stabilizing/destabilizing as a function of pressure. In particular, we identify novel phases of BaSi, BaSi2, BaSi3, and BaSi5 that might be synthesizable experimentally over a wide range of pressures. Chapter 4 contains the investigation of the phases diagram of the N–H–O system. By using ab initio evolutionary structural search, we report the prediction of two novel phases of the N–H–O ternary system, namely NOH4 and HNO3 (nitric acid) at pressure up to 150 GPa. Our calculations show that the new C2/m phase of NOH4 is stable under a large range of pressure from 71 GPa to 150 GPa while the P21/m phase of HNO3 (nitric acid) is stable from 39 GPa to 150 GPa (the maximum pressure which we have studied). We also confirmed that the composition NOH5 (NH3H2O) becomes unstable for pressures above 122 GPa. It decomposes into NH3 and H2O at this pressure. Chapter 5 focuses on p-type transparent electrodes of ternary chalcogenides. We use a high-throughput approach based on DFT to find delafossite and related layered phases of composition ABX2, where A and B are elements of the periodic table, and X is a chalcogen (O, S, Se, and Te). From the 15 624 compounds studied in the trigonal delafossite prototype structure, 285 are within 50 meV/atom from the convex hull of stability. These compounds are further investigated using global structural prediction methods to obtain their lowest- energy crystal structure. We find 79 systems not present in the "Materials project database" that are thermodynamically stable and crystallize in the delafossite or in closely related structures. These novel phases are then characterized by calculating their band gaps and hole effective masses. This characterization unveils a large diversity of properties, ranging from normal metals, magnetic metals, and some candidate compounds for p-type transparent electrodes. At the end of the thesis, we give our general conclusion and an outlook
MacKain, Olivier. « Modélisation du maclage à l’échelle atomique dans les métaux hexagonaux : germination et migration de disconnections dans le zirconium, le titane et le magnésium ». Thesis, Lyon, 2017. http://www.theses.fr/2017LYSE1134/document.
Texte intégralThe aim of this thesis is to identify and quantify the parameters of importance when dealing with twin thickening in three hcp metals (Zr, Ti, Mg). The mechanism we study is the glide of twinning dislocations, i. e. the disconnection, along the perfect twin boundaries. We first focus on the nucleation of disconnection before addressing their migration. A study using an EAM potential allows us to validate an original coupling between our atomistic simulations and linear elasticity in order to extract the core energy of disconnection.We then show how this coupling permits to divide the formation energy in two terms: the core contribution, intrinsec to the disconnections, and an elastic one, which depends on the disconnection's environment. Thanks to this partition, we model the formation of isolated disconnection that may appear along the different twin planes. We select the dipoles of lowest formation energies in order to perform ab initio calculations and compare the behavior observed the three different metals. We then model the migration of disconnections along the perfect twin planes. To do so, we use the Nudged Elastic Band method, and find out that the migration energy of disconnections is one order of magnitude lower than their formation energies. We therefor conclude that the disconnection nucleation is the rate limiting factor to explain twin thickening thanks to the creation and motion of disconnection
Liang, Liang. « Simulation ab initio des défauts étendus du Ti & ; en présence d'interstitiels H et O ». Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLX009/document.
Texte intégralABSTRACT: The aim of this thesis is to study the influence of hydrogen or oxygen solutes on extended defects in alpha titanium by ab initio calculation. Results are divided into three parts. In a first part the octahedral interstitial site of alpha-Ti is found energetically more favorable for a H or an O atom. The presence of H increases the volume while O has the opposite effect. The presence of H slightly decreases the elastic constants of alpha-Ti while O has an opposite effect. In a second part two new SFs are found: 0.57·(c+a) on π2 and 0.215·[1-102] on π1 plane. The second one is related to the low formation energy of the {10-11} twin boundary. A c+a screw dislocation 3-part dissociation mechanism is proposed. However the c+a screw core tends to spread differently according to the initial core position and a complete 3-part dissociation is not found, which may mean that such a dissociation is not easily obtainable from an initially perfect dislocation core. As segregation to SF means a decrease of the SF energy, the presence of O may make the SF formation energetically more difficult, contrary to H case. H strongly segregates to the a screw dislocation core region with segregation energies varing from 0.06 to 0.3 eV while O hardly segregates to it. Both H and O in core sites change the meta-stable gliding prismatic dissociation to π1 plane or a prism-π1 plane mixed configuration. According to our measurements of Peierls energy barriers with H or O in different sites and concentrations, H makes the gliding more difficult, thus increasing the CRSS in prismatic plane, in agreement with experimental measurements. The effect of H is not big enough to induce a cross-slip of the gliding a-screw dislocation to the π1 plane and that screw will prefer to keep on gliding in its same prismatic plane. The Peierls energy barrier is extremely increased when an O is present in the core position, much higher than the barrier for π1 plane glide or a glide in the nearest prismatic plane. A cross-slip could happen in this case. In the last part, three different deformations are applied to TBs. Their structural stabilities depend not only on their intrinsic characters at the atomistic level but also on the deformation mode applied. {10-12}, {11-22} TB structures fail for deformations as low as 1% or 2% along the c-axis. The {11-21} and the {10-11} TBs are much more resistant. The presence of segregated H and O enhances the {10-12} and {11-22} TB limited stability. A twinning disconnection dipole model is proposed which allows the simulation of a TD in a size limited supercell. Segregation energy calculations with the {10-12} TB and its TD validate the model at the TB level and show that H and O should distribute more or less homogeneously to the TD core and the TB, with only a slight preference to the TD core although not at the interstitial sites of the atomic layer related to the disconnection step itself
Cotfas, Nicolae. « Modèles mathématiques pour cristaux et quasicristauxX ». Grenoble INPG, 1998. http://www.theses.fr/1998INPG0130.
Texte intégralLivres sur le sujet "Cristallographie Quantique"
Guymont, Michel. Structure de la matière : Atomes, liaisons chimiques et cristallographie. Paris : Belin, 2003.
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