Дисертації з теми "Théorie de la structure électronique"
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Krzeminski, Christophe. "Structure électronique et transport dans une jonction moléculaire." Phd thesis, Université des Sciences et Technologie de Lille - Lille I, 2001. http://tel.archives-ouvertes.fr/tel-00600434.
Trambly, de Laissardière Guy. "Etude théorique de la structure électronique des matériaux quasicristallins." Université Joseph Fourier (Grenoble), 1996. http://www.theses.fr/1996GRE10075.
Habar, Mustapha. "Contribution à l'étude de la structure géométrique et électronique de matériaux massifs, de surfaces et d'interfaces." Mulhouse, 1989. http://www.theses.fr/1989MULH0114.
Sottile, Francesco. "Fonctions de réponse des semi-conducteurs et des isolants : de l'équation de Bethe-Salpeter à la théorie de la fonctionnelle de la densité dépendante du temps." Phd thesis, Ecole Polytechnique X, 2003. http://tel.archives-ouvertes.fr/tel-00007531.
Borsalino, Dimitri. "Molécules polaires ultra-froides : structure électronique et contrôle optique." Thesis, Paris 11, 2015. http://www.theses.fr/2015PA112232/document.
This thesis deals with ultracold molecules research, which interest has been growing for several years. Unlike atoms, laser-cooling molecules is very difficult. Alternative methods are necessary to be searched for in order to create ultracold molecular gases. This theoretical work focuses on a particular type of heteronuclear diatomic molecules, possessing an intrinsic electric or magnetic dipole moment, from which originates their mutual anisotropic interactions.Based on the precise knowledge of KRb and KCs molecules (possessing a significant intrinsic electric dipole moment) spectroscopy, combined with theoretical results, the cooling of their internal degrees of freedom using Stimulated Raman Adiabatic Passage (STIRAP), a laser process bringing molecules towards their absolute ground state, has been modelled. Several STIRAP schemes have been investigated and compared regarding their efficiency. The RbCa molecule has then been studied, which spectroscopy is still unknown. The ability of controlling the anisotropic interactions induced by the simultaneous presence of an electric and magnetic dipole moment provided by this species is a clear advantage. The electronic structure of RbCa has been computed with two methods, thus allowing to estimate the reliability of the results. A scheme of laser transitions bringing to the formation of cold RbCa molecules from separate atoms has been proposed.Manipulating and trapping molecules relies on the precise knowledge of their response to an external electromagnetic field, characterised by their dynamic dipolar polarisability. The quantum chemistry calculations mentioned earlier allowed us to compute high-lying excited states, dynamic polarisability has then been computed for a whole set of diatomic molecules (alkali dimers, RbCa, RbSr, …). The optimal parameters for trapping those molecules has then been determined
Tazi, Mouhsine. "Détermination de champs de forces de la porphine et des métalloporphines à l'aide de la théorie de la fonctionnelle de densité et leur validation par le calcul des intensités Raman de résonance." Lille 1, 2000. http://www.theses.fr/2000LIL10135.
Cortona, Pietro. "Théories des fonctionnelles de la densité : nouvelles approximations et applications." Paris 11, 1987. http://www.theses.fr/1987PA112286.
We extended the applicability range of the density-functional theory to the case of relativistic spin-polarized systems. The difficulty of this case is due to the fact that the spin polarisation and the spin orbit effect together break the degeneracy of the system; so neither the total angular momentum j, nor its orbital part L are good quantum numbers of the system. This last point implies that the only way of writing the wave functions is by an infinite series of Dirac orbitals. However, this difficulty can be circumvented: we indicated a method to obtain an explic1te solution in the atomic case. By this method, which can be extended to treat solids, we studied the magnetic properties of the trivalent rare earth ions. We have also proposed a new approximation to the exchange part of the exchange-correlation energy functional. Our approximation treats exactly the self-interaction terms and uses, in a more consistent way than other analogous methods, the homogeneous gas theory in order to obtain an approximate expression of the inter-electron exchange energy. We tested our method by extensive calculations of the electronic properties of many atomic systems: the results show a systematic Improvement both of the local-density and the other self -interaction-corrected results. Next, we extended our method in order to treat relativistic systems. This can be immediatly obtained alter deriving the relativistic inter-electronic exchange energy expression for the homogeneous gas. Using the version of the theory, we showed that the local-density approximation is not appropriate to study solids containing heavy elements. Finally, we studied the charge distributions of solids of alkali halides. We were mainly interested into the ionic deformations due to the crystal field: so we determined the structure factors of these solids by a band calculation in the local-density approximation and we compared these results both with the experimental and with theoretical free-ions results. Ln this wag, we were able to show that the anions in the solids contract; on the other hand our calculations showed that the simple local-density approximation is sufficient to study charge density in ionic solids
Boyer, Richard Soline. "Modélisation physique de la structure électronique, du transport et de l'ionisation par choc dans les matériaux IV-IV massifs, contraints et dans les puits quantiques." Paris 11, 2004. https://tel.archives-ouvertes.fr/tel-00008310.
This PhD thesis is devoted to the study of physical phenomena in SiGe devices involving high energy carriers which induce impact ionization. A thirty-band k. P method has been developed to model energy band diagrams of bulk and strained Si, Ge and SiGe alloys on the whole Brillouin zone in a large energy range (11 eV around the band gap). This method provides the Luttinger parameters and the conduction band effective masses with a very good accuracy. Associated with an envelop function algorithm, the band diagrams of SiGe quantum wells have been obtained in the valence and in the conduction band. From these electronic structures, carrier densities of states are obtained in bulk and strained semiconductors and in quantum wells. Hole density of state masses in bulk and strained SiGe alloys have been calculated as a function of crystal temperature. Chapter 4 is devoted to transport study in SiGe alloys with a matrix resolution of the Boltzmann transport equation. From the density of state masses, hole mobilities are calculated in SiGe alloys. From high electric field transport simulation, impact ionization coefficients have been evaluated for electrons in strained Si and for holes in strained Ge. Electroluminescence measurements have been performed on SiGe HFET and IMPATT diodes. The impact ionization coefficient calculated with the solver are in the same range as the experimental data
Kenzari, Hocine. "Structure électronique des composés à grande maille de type « chimney-ladder »." Vandoeuvre-les-Nancy, INPL, 1998. http://www.theses.fr/1998INPL121N.
Lacoste, Marc. "Complexes réservoirs d'électron mono-et binucléaires : aspects électroniques et structuraux : transfert d'électron induit par effet de sel." Bordeaux 1, 1987. http://www.theses.fr/1987BOR10633.
Magné, Damien. "Synthèse et structure électronique de phases MAX et MXènes." Thesis, Poitiers, 2016. http://www.theses.fr/2016POIT2284/document.
The aim of this work is at first to study the electronic structure of bidimensional titanium carbide systems, belonging to the MXene family and also to synthesize thin films of such new materials to characterize their properties. The study of the electronic structure has been performed for the Ti3C2T2 MXene with a special attention to the T surface groups by using a combination of electron energy loss spectroscopy and ab initio calculations. This study, focused on both valence and core electrons excitations, enabled the identification of the surface group localization, their influence on the MXene electronic structure as well as their chemical nature. The limits of our TEM-based study is also discussed in view of irradiation phenomena which induce the loss of hydrogen atoms. The synthesis of a MXene thin film requires, beforehand, that of a MAX phase thin film: we opted for Ti2AlC, the precursor for the Ti2C MXene. The MAX phase thin film synthesis was carried out by ex-situ annealing of a multilayer layers. X-ray diffraction experiments and cross-sectional transmission electron microscopy observations show that a highly textured Ti2AlC thin film is obtained above 600°C after the formation, at 400°C, of a metastable solid solution. Finally, by using the same process for V2AlC, we demonstrate that the initial phase orientation plays a key role for the texture of the thin film so obtained
Duhot, Sylvie. "Transport électronique non local dans des structures hybrides supracondctrices." Phd thesis, Grenoble 1, 2008. http://www.theses.fr/2008GRE10157.
In this thesis, we study various hybrid structures with superconducting parts. The first chapter analyzes non local transport in normal metal (N) - superconductor (S) - normal metal structures. We consider one dimensional model for the N-S-N junctions using either the Blonder-Tinkham-Klapwijk method, or the Green’s functions techniques. We find that non local transport can be enhanced by multiple scattering processes in the normal regions in a similar way as in the phenomenon of “reflectionless tunnelling”. In the second chapter, we consider a nanoscale SQUID formed of a carbon nanotube coupled to superconducting electrodes. Non local processes decrease the critical current and introduce sample to sample fluctuations in the current-phase relation. In the third chapter, we study the correlations of current fluctuations in superconducting multiterminal structures with semiclassical Boltzmann-Langevin theory. The multiple Andreev reflections can give a change of sign in crossed correlations for certain range of parameters. In the last chapter, we analyze hybrid systems involving superconductors and charge density wave (CDW) compounds. We find that the Cooper pair can penetrate in the CDW just on Fermi wavelength. So, the S-CDW-S junction does not transport supercurrent
Duhot, Sylvie. "Transport électronique non local dans des structures hybrides supracondctrices." Phd thesis, Université Joseph Fourier (Grenoble), 2008. http://tel.archives-ouvertes.fr/tel-00343716.
Le premier chapitre analyse le transport non local dans une structure métal normal – supraconducteur – métal normal (N-S-N). Nous considérons un modèle unidimensionnel pour les jonctions N-S-N soit à l'aide de la méthode de Blonder-Tinkham-Klapwijk soit à l'aide des techniques des fonctions de Green. Nous trouvons que le transport non local est amplifié par les processus d'interactions multiples dans les électrodes normales, comme pour le phénomène de “reflectionless tunnelling”.
Dans le second chapitre, nous considérons un SQUID à l'échelle nanoscopique formé d'un nanotube de carbone couplé à des électrodes supraconductrices. Les processus non locaux
diminuent le courant critique et introduisent des fluctuations d'échantillon à échantillon dans la relation courant-phase en fonction des paramètres du modèle.
Dans le troisième chapitre, nous étudions les corrélations des fluctuations de courant dans des structures supraconductrices multiterminales à l'aide de la théorie semiclassique de Boltzmann-Langevin. Les réflexions d'Andreev multiples peuvent donner un changement de signe dans les corrélations croisées pour certains paramètres.
Dans le dernier chapitre, nous analysons des systèmes hybrides avec des supraconducteurs et des ondes de densité de charge (ODC). Nous trouvons que les paires de Cooper ne peuvent pénétrer dans les ODC que sur la longueur d'onde de Fermi. Ainsi, les jonctions S-ODC-S ne peuvent pas transporter de supercourant.
Ben, Abdellah Abdellatif. "Contribution à l'étude des propriétés de transport électronique d'alliages liquides à base de manganèse et de transport électronique et atomique du système gallium-plomb présentant une lacune de miscibilité." Metz, 1994. http://docnum.univ-lorraine.fr/public/UPV-M/Theses/1994/Ben_Abdellah.Abdellatif.SMZ9441.pdf.
The aim of this thesis is to study the transport properties of liquid transition metals alloys and the atomic transport properties of the Ga-Pb system which exhibits a miscibility gap. We have measured the electrical resistivity of Al-Mn liquid alloys, which, is quasicristaline, in the solid state. We have also extended this investigation to Ga-Mn and Zn-Mn in order to examine the electrical resistivity evolution as a function of the position of the polyvalent metal in the periodic table. The resistivity has been calculated with the phases shifts m(Ef). Our calculation is based on two possible electronic configurations of manganese and two exchange treatments. We have improved our results in taking into acount the energy dependance of phase shifts and using the Fermi energy obtained by a fit on the experimentals resistivities of pure metals. In addition, we propose a simple method to determine the boundary of a miscibility gap for Ga-Pb system. The optimized phase diagram for Ga-Pb has been obtained by using the square-well potential. The purpose of the last part is the use of a new experimental technique to measure the interdiffusion coefficient in the non dilute binary Ga-Pb, which exhibits a miscibility gap. This technique is based on the use of a finite capillary to measure the resistivity of different section of the capillary enabling us to deduce the concentration profile
Fadjie, Djomkam Alain Bruno. "Étude des propriétés électroniques des monocouches moléculaires greffées sur des substrats nSi(111)." Rennes 1, 2011. http://www.theses.fr/2011REN1S102.
Electrical transport in ultrathin Metal-Insulator-Semiconductor (MIS) tunnel junctions is analyzed using the temperature dependence of current voltage and admittance spectroscopy measurements applied to Hg // ML – n Si junctions. The coverage and thickness of molecular layers (-CnH2n+1, -C10H20-COOH) covalently bonded to Si(111), before and after capping with clusters (Se8Re6(TBP)4(OH)2, Mo6Br8F6), are deduced from XPS and ellipsometry. The I(V) characteristics are described using a new model for transport in ultrathin MIS junctions. We observe that functional groups (acid, clusters) modify the electronic structure of the junction and consequently the I(V) characteristics. In the low forward bias regime governed by thermionic emission, the observed linear T-dependence of the effective barrier height provides the thermionic emission barrier height and the tunnel barrier attenuation. In the high-forward-bias regime, the bias dependence of the tunnel barrier transparency is approximated by a modified Simmons model for a rectangular tunnel barrier. The density distribution of defects localized at the ML / Si interface is deduced from admittance data (low-high frequency method) and from a simulation of the response time τR(V) using a model for a non equilibrium tunnel junction. The low density of electrically active defects near mid-gap indicates a good passivation of dangling bonds at the ML / Si interface
Landron, Sylvain. "Etude ab initio de la structure électronique des oxydes de cobalt NaxCoO2." Toulouse 3, 2008. http://thesesups.ups-tlse.fr/273/.
(The NaxCoO2 Cobalt oxides are compounds with many interesting properties. In this work we were particularly interested in two compounds of the family: firstly, the Na0. 3CoO2-1. 3H2O which presents a superconducting phase, secondly the x=0. 5 system which presents an insulator to metal phase transition at 52 K and a rich phase diagram as a function of temperature and magnetic field. Using ab initio calculations molecular spectroscopy methods applied on fragments embedded in an appropriate bath, we presented the determination of simple models as well as the evaluation of the effective interactions for these two interesting compounds. We also studied the cobalt 3d-shell splitting under the trigonal distortion observed in these compounds. This analysis led to reasons for which some results, like the ones issued of ligands field theory and some issued of density functional calculations, yield an orbital splitting in disagreement with experimental results
Truflandier, Lionel. "Détermination de paramètres RMN par la théorie de la fonctionnelle de la densité : application aux éléments 3d en RMN de l'état solide." Nante, 2007. http://www.theses.fr/2007NANT2083.
Besides Zeeman levels perturbation, nuclear magnetic resonance spectroscopy (NMR) applied to solid state allows the observation of numerous coupling interactions that are not accessible in liquid state. Despite sequential developments for high resolution measurements, interpretation of resonance spectra remains delicate. .
Nour, Safouh. "Développements de la méthode MS-LSD vers le calcul de la structure électronique d'agrégats contenant des atomes lourds et des semiconducteurs." Lyon 1, 1991. http://www.theses.fr/1991LYO19009.
Jraij, Alya. "Etude théorique de la structure et des propriétés électronique de différents composés d'alcalins." Lyon 1, 2003. http://www.theses.fr/2003LYO10047.
Boutassetta, Nabil. "Prédiction théorique de la structure électronique de molécules diatomiques comportant un alcalino-terreux." Lyon 1, 1997. http://www.theses.fr/1997LYO10127.
Mahmoud, Salman. "Étude théorique des molécules diatomiques BN, SiN et LaH, structure électronique et spectroscopie." Thesis, Montpellier 2, 2014. http://www.theses.fr/2014MON20080/document.
In the present work a theoretical investigation of the lowest molecular states of BN, SiN and LaH molecule, in the representation 2s+1Λ(+/-), has been performed via complete active space self-consistent field method (CASSCF) followed by multireference single and double configuration interaction method (MRSDCI). The Davidson correction noted as (MRSDCI+Q) was then invoked in order to account for unlinked quadruple clusters. The entire CASSCF configuration space was used as a reference in the MRCI calculation which has been performed via the computational chemistry program MOLPRO and by taking advantage of the graphical user interface Gabedit. Forty-two singlet, triplet, and quintet lowest electronic states in the 2s+1Λ(+/-) representation below 95000 cm-1 have been investigated of the molecule BN. While twenty-eight electronic states in the representation2s+1Λ(+/-)up to 70000 cm-1 of the SiN molecule have been investigated.On the other hand the Twenty four low-lying electronic states of LaH in the representation 2s+1Λ(+/-) below 35000 cm-1 have been studied by two different methods and by taking into consideration the spin orbit effect of the molecule LaH we give in the energy splitting of the eight electronic states. The potential energy curves (PECs) together with the harmonic frequency ωe, the equilibrium internuclear distance re, the rotational constants Be and the electronic energy with respect to the ground state Te have been calculated for the considered electronic states of BN, SiN and LaH molecule respectively. Using the canonical functions approach, the eigenvalues Ev, the rotational constants Bv ,the centrifugal distortion constants Dv and the abscissas of the turning points Rmin and Rmax have been calculated for electronic states up to the vibrational level v =51 for LaH molecule.Eighteen and Nine electronic states have been investigated here for the first time for the molecules of BN and SiN respectively, while for LaH, news results are performed for twenty three electronic states of LaH molecule and the spin-orbit effect of LaH molecule is given here for the first time. A comparison with experimental and theoretical data for most of the calculated constants demonstrated a very good accuracy. Finally, we expect that the results of our work should invoke further experimental investigations for these molecules. Our results have been published in Canadian journal of chemistry, Journal of Quantitative Spectroscopy and Radiative Transfer and we have two other papers in preparation to submit
Poiré, Yannick. "Etude la C. E. M. Des alimentations à découpage pour systèmes embarqués : Conception et optimisation des structures de filtres d'entrée." Rennes, INSA, 2007. http://www.theses.fr/2007ISAR0032.
Nanot, Sébastien. "Structure de bandes et transport électronique dans les nanotubes de carbone sous champ magnétique intense." Toulouse 3, 2009. http://thesesups.ups-tlse.fr/625/.
Electronic transport measurements in individual multiwall carbon nanotubes under pulsed magnetic field (60T) are presented in this PhD thesis. The purpose is to observe modulations of the electronic dispersion by the magnetic field. High quality nanotubes are contacted with short distances between contacts. This allows to reach quasi-ballistic and slightly diffusive transport regimes occurring mainly on the outer wall. Transistor configuration enables to modulate the charge carrier energy (Fermi level) through many subbands by an electrostatic potential ("a gate"). In order to clarify the contribution of innermore shells, a spectroscopic Raman study is first presented. A strong variation from wall to wall of the intensity of charge transfer between successive shells is unraveled. The study under magnetic field of nanotubes with semiconducting and metallic outer wall is then presented. When the magnetic field is applied perpendicularly to the axis of the nanotube, the onset of propagating Landau states is unveiled. This induces modulations of resonance conditions in an electronic Fabry-Pérot type regime, closing of the energy gap in a semiconducting shell and reintroduction of backscattering in a metallic one. This last effect comes with a pinning of the Fermi level to the Landau one gathering at zero energy under high field. Those results are in agreement with theoretical models taking into account an homogeneous disorder. Finally, the Aharonov-Bohm effect under many periods and many subbands is observed when the field is parallel to the axis of the nanotube. The metallicity of the outer wall and the correspondence between the gate voltage and the charge carrier energy are obtained by comparing the experimental conductance oscillations with a model obtained in the perfect case. To describe further the magneto-fingerprints, transmission lowering at the contacts and due to defects are qualitatively considered
Guézo, Sophie. "Microscopie à Emission d’Electrons Balistiques (BEEM) : étude des propriétés électroniques locales d’hétérostructures." Rennes 1, 2009. https://tel.archives-ouvertes.fr/tel-00429321.
This thesis work has been developed on ballistic electron emission microscopy (BEEM) under ultra-high vacuum, dedicated to the study of interface electronic properties of heterostructures based on III-V semiconductors, essentially for further potential applications in spintronics. First, the study of Au/GaAs Schottky junction has shown, by comparison between experimental measurements and theorical calculations, the effect of structural properties on hot-electron transport. A similar study realized on Fe/GaAs(001) has confirmed the BEEM sensitivity to electronic structure effects. Then, BEEM measurements on the barrier MgO/GaAs(001) have revealed new conduction channels localized in the band gap of MgO. They are related to oxygen vacancies in the oxide layer, which strongly reduce the tunnel barrier height. Finally, first measurements of spin-polarized hot-electron transport realized on Fe/Au/Fe/GaAs(001) spin-valve are presented
Chanier, Thomas. "Propriétés magnétiques et structure électronique des semi-conducteurs magnétiques dilués de type II-VI." Phd thesis, Université de Provence - Aix-Marseille I, 2008. http://tel.archives-ouvertes.fr/tel-00363983.
L'étude ab initio des couplages d'échange entre deux ions magnétiques premiers voisins montre l'insuffisance de la fonctionnelle LSDA (approximation de la densité locale polarisée en spin) pour décrire l'état fondamental des DMS. Grâce à la LSDA+U, qui prend en compte la corrélation forte des électrons des couches 3d des métaux de transition par une correction de type Hubbard, on obtient des constantes d'échange d-d antiferromagnétiques (AFM) de l'ordre de quelques meV pour les composés à base de Co et Mn non-dopés électriquement. Le dopage de type p permet d'obtenir des températures de Curie ferromagnétiques (FM) de l'ordre de 100 K. Les valeurs LSDA+U des couplages d'échange sp-d N\alpha (N\beta) entre électrons (trous) de la bande de conduction (de valence) et impuretés magnétiques sont FM (AFM) de l'ordre de 0.1 eV (-1 eV). Un modèle analytique de la structure électronique des DMS montre la présence d'un état localisé séparé de la bande de valence dans les composés à base de ZnO (N\beta fortement AFM) due à l'hybridation forte entre les états 3d de l'impureté magnétique et la bande de valence.
L'état fondamental des lacunes neutres isolées dans les semi-conducteurs II-VI est examiné par une combinaison de calculs ab initio et analytiques. On montre que la lacune de Zn dans ZnO porte un spin S=1 en accord avec l'expérience. Dans les autres composés II-VI moins ioniques, cet état triplet est quasi-dégénéré avec un état singulet de spin nul. Les lacunes d'anions sont non-magnétiques.
Lachekar, Hassane. "Transfert des paramètres de densité électronique et applications." Nancy 1, 1997. http://www.theses.fr/1997NAN10209.
Fathallah, Sofiane. "Étude théorique de la structure électronique et de propriétés physiques d'édifices moléculaires à ponts carbonés." Rennes 1, 2005. http://www.theses.fr/2005REN1S139.
Deleurence, Amélie. "Modélisation mathématique et simulation numérique de la structure électronique de cristaux en présence des défauts ponctuels." Phd thesis, Ecole des Ponts ParisTech, 2008. http://pastel.archives-ouvertes.fr/pastel-00004782.
Maurat, Emmanuel. "Étude théorique de la dynamique de charge et de spin de structures électroniques confinées." Strasbourg, 2009. https://publication-theses.unistra.fr/public/theses_doctorat/2009/MAURAT_Emmanuel_2009.pdf.
In this first approach, the dynamic aspects are modeled using concepts of statistical mechanics at the thermodynamic equilibrium. By using the Local Spin Density Functional Theory (LSDA-DFT) at finite temperature and within the grand canonical ensemble, we have studied the magnetic properties of small metal particles with open-shell structures made up of elements which are no magnetic in the bulk (like the noble metals Ag, Au or Pt). As for ferromagnetic bulk materials, these nano objects present a ferromagnetic-paramagnetic second order phase transition at a critical temperature which depends heavily on their size and on the electronic correlations. We have shown that the magnetic susceptibility obeys the Curie-Weiss law. This result is due to the finite size of the system implying a discrete spectrum of electronic levels and is consistent with recent measurements on aggregates of platinum sorted by mass [109]. Thus, when the electron temperature increases sharply, the magnetization decreases. Then, through the electron-phonon coupling the thermal energy is distributed over the lattice, which in turn decreases the electron temperature and allows the resurgence of the magnetization. This analysis is supported by some experimental results as the fact that the demagnetization is more or less pronounced according to the Curie temperature of the material [130]. Thanks to the linear response theory for LSDA-DFT that we developed, we were also able to find the features of a such demagetization on optical spectrums. However, this model is only qualitative. Indeed, the mechanisms that are causing the phenomenon of demagnetization are hidden by the statistical treatment of the problem. The spin magnetic moment (which, for metals, is essential to the magnetization of the system) may be redistributed on the orbital moment via spin-orbit coupling. The latter is of relativistic origin and must be added to the non-relativistic Hamiltonian describing the usual light-matter interaction. A few years ago, this hypothesis had already been discussed by G. P. Zhang and W. Hübner [149] to explain the demagnetization in ferromagnetic films. However, it was later refuted by B. Koopmans [131] ; the parameters used in [149] are not compatible with those used in experiments. First, in order to make us our own ideas on the subject and second, to extend to finite systems the studies conducted for the bulk, we have investigated the effect of spin-orbit coupling on the spin dynamics in nanoparticles. To this end, still using the jellium model (assuming a purely electronic processus), we choosed the TDDFT approach (Time Dependent Density Functionnal Theory) which have been completed by the introduction of the spin-orbit coupling term. We have thus observed that the spin-orbit coupling is a good mechanism for demagnetization, but it is not sufficient to explain the experimental observations. Indeed, as confirmed by a recent publication [? ], the quantity of orbital angular momentum is not a good reservoir to absorb the amount of spin angular momentum coming from the demagnetization. However, if the mechanism induced by the spin-orbit coupling is not sufficient to explain the full demagnetization, it is necessary as explained in the last part. In addition, we were able to highlight the important role played by the polarization of the laser pulse in the demagnetization process. This last aspect has been recently confirmed experimentally [138]. In the very last part of the manuscript, we propose a microscopic mechanism allowing to go beyond mean field which involves jointly the electron-electron collisions, the spin-orbit coupling and the conservation of total angular momentum. A diagram of the algorithmic model is proposed to allow its implementation in a standard TDDFT approach. Indeed, we believe that a redistribution of angular momentum induced by electron collisions must play a crucial role in the demagnetization phenomenon and all the more so that (i) the electronic temperatures, because of the interaction with the laser, are very high, and (ii) the highly nonlinear processes of electron collisions
Diarra, Mamadou. "Etude théorique de nanofils semiconducteurs." Phd thesis, Université des Sciences et Technologie de Lille - Lille I, 2009. http://tel.archives-ouvertes.fr/tel-00432564.
Diarra, Mamadou Marcel. "Étude théorique de nanofils semiconducteurs." Electronic Thesis or Diss., Lille 1, 2009. http://www.theses.fr/2009LIL10010.
Recent breakthroughs in the growth of semiconductor nanowires (SNWs) have opened up great opportunities for nanoscale device applications. SNWs remain semiconducting independent oftheir diameter and orientation, giving the ability to control their properties by doping. Therefore a large number of experimental works have addressed the problem of doping and of its modulation in SNWs. While there is no doubt that p- and n-type SNWs can be produced, the question of how their electrical conductivity depends on the doping level remains largely open. ln fact, most of the works showing good transport properties concern SNWs doped with high impurity concentration, near or above the Mott density. ln order to investigate the doping efficiency in SNWs, we present calculations of the electronic structure of donor and acceptor impurities in Si nanowires. We show that their ionization energy increases due to the confinement, the quantum confinement at small sizes (diameter < 5 nm) and above aIl the so-called dielectric confinement which occurs when there is an important dielectric mismatch between the wire and its surrounding. For SNWs embedded in a material with a low dielectric constant, we obtain that the impurities cannot be ionized at room temperature even for diameters up to several tens of nanometers. We explain the origin of this behavior by considering the effect of the impurity potential and of the self-energy of the carrier, and we make predictions for the ionization energy in different configurations. These results allow us to conclude on the necessity to use heavy doping to obtain good electrical properties in SNWs
Niquet, Yann Michel. "Etude des propriétés de transport de nanostructures de semiconducteurs." Lille 1, 2001. https://pepite-depot.univ-lille.fr/LIBRE/Th_Num/2001/50376-2001-171.pdf.
Karoui, Sondès. "Influence du magnétisme sur les propriétés structurales et énergétiques du système cobalt-platine : une étude théorique." Paris 6, 2013. http://www.theses.fr/2013PA066772.
Due to their magnetic properties, Co-Pt nano-alloys are the subject of various studies, in particular regarding the influence of the size of the nanoparticle on the order-disorder transition. In this context, a fundamental question is whether or not magnetism plays an important role in order phenomena, and if yes, how to implement it simply in an inter- atomic potential. By combining ab initio calculations and a tight binding semi-empirical model that we have developed, we were able to identify the importance of magnetism on the structural properties of these alloys. Thus, our ab initio study has shown that mag- netism is an essential driving force for the stability of chemical order in the bulk alloys of the Co-Pt system. With the help of our energetics model, we were able to reproduce not only the electronic properties of cobalt and platinum but also the principal magnetic properties (such as the magnetic transition) of cobalt. Furthermore, in the bulk case, the energy gain due to magnetism is correctly estimated in tight binding. We have equally demonstrated a softening of the elastic constants under magnetic effects. Finally, an in- fluence of magnetism on Co surfaces along the (001) and (111) orientations was observed, which in consequence strongly favors the segregation of cobalt to the surface (for both orientations). Magnetism equally reinforces the segregation of cobalt in the second plane, thus entering into competition with order phenomenon
Mharchi, Ahmed. "Etude théorique de la structure électronique du siliciure d'erbium, épitaxie sur Si (111) dans le cadre de l'extension cristalline de la méthode de Hückel étendue." Mulhouse, 1995. http://www.theses.fr/1995MULH0378.
Guitou, Marie. "Etude théorique de la structure de composés moléculaires de métaux lourds." Marne-la-Vallée, 2002. http://www.theses.fr/2002MARN0150.
Muthali, Ajmalghan. "Calculs de structures électroniques et modèles thermodynamiques pour les matériaux d'intérêt énergétique." Electronic Thesis or Diss., Aix-Marseille, 2019. http://www.theses.fr/2019AIXM0353.
ITER - International Thermonuclear Experimental Reactor - is built in Cadarache, is designed to demonstrate the feasibility of controlled nuclear fusion on earth for the production of clean and sustainable energy. Tungsten (W), the chosen plasma facing-material (PFM) for divertor will be irradiated by a high flux of particles including hydrogen isotopes (HIs) during its operation. Several fundamental issues related to the operation of ITER remain open, including questions concerning the interaction HI and PFM which damages the surface of the vessel, increases the risk of hazard and prevents fusion from occurring. This is the aim of this Ph.D. thesis by means of electronic structure calculations within the density functional theory (DFT). While the manuscript consists of six chapters, it can be grouped into three main parts. In the first one, we investigate hydrogen coverage on the tungsten W(110) and W(100) surfaces via periodic DFT, providing the most stable configurations that hydrogen forms on the surface, step-wise, from the bare surface up to saturation. Since DFT data are only valid at a temperature of 0K, we followed in the second part a statistical approach to make the surface coverage temperature and pressure dependent. In the last part of this document, we focus on the mechanism of hydrogen diffusion in the sub-surface and on the recombination of molecular hydrogen on top of both surfaces. In particular, we explore the surface-coverage dependency of these mechanisms and how it affects their energetics and related kinetics
Diarra, Mamadou Marcel. "Étude théorique de nanofils semiconducteurs." Thesis, Lille 1, 2009. http://www.theses.fr/2009LIL10010/document.
Recent breakthroughs in the growth of semiconductor nanowires (SNWs) have opened up great opportunities for nanoscale device applications. SNWs remain semiconducting independent oftheir diameter and orientation, giving the ability to control their properties by doping. Therefore a large number of experimental works have addressed the problem of doping and of its modulation in SNWs. While there is no doubt that p- and n-type SNWs can be produced, the question of how their electrical conductivity depends on the doping level remains largely open. ln fact, most of the works showing good transport properties concern SNWs doped with high impurity concentration, near or above the Mott density. ln order to investigate the doping efficiency in SNWs, we present calculations of the electronic structure of donor and acceptor impurities in Si nanowires. We show that their ionization energy increases due to the confinement, the quantum confinement at small sizes (diameter < 5 nm) and above aIl the so-called dielectric confinement which occurs when there is an important dielectric mismatch between the wire and its surrounding. For SNWs embedded in a material with a low dielectric constant, we obtain that the impurities cannot be ionized at room temperature even for diameters up to several tens of nanometers. We explain the origin of this behavior by considering the effect of the impurity potential and of the self-energy of the carrier, and we make predictions for the ionization energy in different configurations. These results allow us to conclude on the necessity to use heavy doping to obtain good electrical properties in SNWs
Gamboa, Ramirez Stefani. "Structure-function relationship in polynuclear bio-inspired copper complexes : combined experimental and computational studies." Electronic Thesis or Diss., Aix-Marseille, 2023. http://theses.univ-amu.fr.lama.univ-amu.fr/230201_GAMBOARAMIREZ_549h879lvul851osvjs537pe_TH.pdf.
Magnetic systems are crucial in many applications, such as data storage, energy conservation, quantum computing, and telecommunications. In this context, polynuclear complexes featuring magnetic interaction between metal ions are a central topic in molecular magnetism. A magnetic interaction becomes operative when the unpaired electron of two or more open-shell centres are in close proximity. This is described by the exchange coupling constant, J, which reports the strength and nature of the interaction. While this observable can be experimentally measured by SQUID, the correct interpretation of the magnetic properties becomes problematic for large systems. In this regard, quantum chemistry has become a crucial tool for the accurate and unique assignment of electronic structures, and Broken-Symmetry (BS) Density Functional Theory (DFT) appears as the method of choice to predict the magnetic interactions due to its applicability for large systems with a low computational cost. Understanding how the structure shapes the exchange interaction in small systems is a first step to being able to describe the magnetic behaviour of larger and more complicated entities. This work combines experimental and theoretical approaches to investigate the magneto-structural correlation and reactivity of dinuclear copper complexes. Upon setting up the appropriate theoretical approach, we applied our methodology to investigate the electronic and magnetic properties of several polynuclear metal complexes, including (i) a trinuclear nickel complex with redox-active ligands, (ii) a tetranuclear nickel complex, and (iii) a nickel-cubane displaying electroactivity towards oxygen evolution reaction
Dorado, Boris. "Etude des propriétés de transport atomique dans le dioxyde d'uranium par le calcul de structure électronique : influence des fortes corrélations." Thesis, Aix-Marseille 2, 2010. http://www.theses.fr/2010AIX22068/document.
Uranium dioxide UO2 is the standard nuclear fuel used in pressurized water reactors. During in-reactoroperation, the fission of uranium atoms yields a wide variery of fission products (FP) which create numerouspoint defects while slowing down in the material. Point defects and FP govern in turn the evolution of the fuelphysical properties under irradiation. In this study, we use electronic structure calculations in order to betterunderstand the fuel behavior under irradiation. In particular, we investigate point defect behavior, as well as thestability of three volatile FP: iodine, krypton and xenon. In order to take into account the strong correlations ofuranium 5f electrons in UO2, we use the DFT+U approximation, based on the density functional theory. Thisapproximation, however, creates numerous metastable states which trap the system and induce discrepanciesin the results reported in the literature. To solve this issue and to ensure the ground state is systematicallyapproached as much as possible, we use a method based on electronic occupancy control of the correlated orbitals.We show that the DFT+U approximation, when used with electronic occupancy control, can describe accuratelypoint defect and fission product behavior in UO2 and provide quantitative information regarding point defecttransport properties in the oxide fuel
Le, Menn Pascal. "Etude de structures intégrées multicouches hyperfréquences utilisant une technologie couches épaisses : application au couplage et au filtrage." Brest, 1990. http://www.theses.fr/1990BRES2014.
Festa, Floriane. "Etude expérimentale et théorique de la structure électronique de l'aluminium en conditions extrêmes par spectroscopie d'absorption X." Phd thesis, Ecole Polytechnique X, 2013. http://pastel.archives-ouvertes.fr/pastel-00904122.
Hamade, Yaman. "Étude théorique de la structure électronique de AlBr, AlI, LuF et LuCl par les méthodes ab-initio." Thesis, Lyon 1, 2009. http://www.theses.fr/2009LYO10169.
Our research concerns the theoretical study of the electronic structure of diatomic molecules such as Aluminum mono-halides AlX (X = Br,I) and Lutetium mono-halides LuX (X = F, Cl). The ab-initio methods are used for our study. These methods SCF, CASSCF (Complete Active-Space Self-Consistent Field) and interaction of configuration multi-reference MRCI with and without Davidson correction. These calculations are performed using the quantum chemistry software package MOLPRO, benefiting from the use of graphic interface GABEDIT. Our findings have consolidated the potential energy curves PECs, spectroscopic constants, including harmonic frequency ωe(cm-1), the internuclear distance at equilibrium Re(Å) and energy Te(cm-1) for a set of singlet and triplet electronic states in the representation 2s +1 Λ (+/-) (neglecting spin-orbit effects) for these four molecules. By comparison between our results and those contributed to the literature, we found a good agreement with a low percentage of error does not exceed 3% from the experimental value was considered as exact
Outerovitch, Robinson. "Études des interactions électroniques effectives dans les solides fortement corrélés." Thesis, université Paris-Saclay, 2022. http://www.theses.fr/2022UPASP156.
The many body quantum problem size grows factorially with respect to the number of elements. In order to treat solids, the DFT uses approximations to reduce the complexity of the problem. However, some materials present properties that are not correctly described by these approximations. This is due to the presence of strong correlations, which are not well taken into account by the standard approximations of DFT.Different methods have been developed to deal with these strong correlations. Some of these methods (DFT+U and DFT+DMFT) propose to calculate exactly the electronic interactions between the electrons of the system which present the most important correlations. These methods require to know the value of the effective interaction between correlated electrons. We use the cRPA, which takes into account the screening effects in materials, to calculate the value of effective interactions.We set up a new implementation of the cRPA allowing to calculate the effective interactions within several correlated orbitals per system. This implementation is then tested against results from the literature. Finally, the calculation of selfconsistent effective interactions in DFT+U /cRPA, leads us to evaluate the relevance of taking into account the correlations on the p-orbitals of the oxygens in the oxides. We show the importance of the choice of correlated orbitals used in DFT+U and we propose, on a physical basis, to use Wannier functions
Etienne, Thibaud. "Développement et application de stratégies d’étude théorique de propriétés remarquables relatives aux états excités moléculaires." Thesis, Université de Lorraine, 2015. http://www.theses.fr/2015LORR0097/document.
Exploiting theoretical methods for modeling remarkable molecular properties has extensively gained interest from the scientific community during the last few decades. The development of these methods has been made possible by the important technological progresses realized in the field of computational science. These advances made accessible some informations that are crucial to our current researches but hitherto impossible to compute. It is thus now possible to solve high-level theoretical issues and to access novel critical properties. Within this framework, quantum-mechanical characterization of molecular excited states still constitutes a challenging achievement with a considerable interest to the theoretical and experimental molecular physics community. However, these studies can be of extreme complexity, due to the interplay between numerous physical phenomena that characterize the access of a system to its own excited states. The scope of our contribution is closely related to these fundamental issues in the sense that we aim at rationalizing the behavior of chromophores facing a photon capture. This light-matter interaction is studied at the molecular level and is addressed in our work with quantum-mechanical methods in order to unravel the mechanisms inherent to the characteristic properties of target compounds. Those interpretations are supported by theoretical developments intending the establishment or consolidation of conceptual and mathematical tools constituting our theoretical strategy for excited states investigations. The aforementioned developments are mostly related to the interaction of chromophores with their molecular vicinity treated implicitely or explicitely, the latter playing an important role in our attempt to gain a geometrical resolution of electronic spectra with conformational space sampling methods. Our interest was also focused on the photoinduced electronic structure reorganization through the design of quantum-mechanical descriptors of excited states topology. On the other hand, applications were related to chromophores exhibiting remarkable molecular properties : solvatochromic probe, explosive probe, chromophore interacting with DNA, dyes designed for third-generation solar cells, multichromophoric clusters
Delaval, Jean-Marie. "Structure et durées de vie radiatives de composés diatomiques du fer et du cuivre : étude théorique de l'autoionisation vibrationnelle dans CO." Lille 1, 1988. http://www.theses.fr/1988LIL10073.
Obeid, Sabah. "Étude théorique de l'ionisation simple de la molécule H3+ : application des fonction d'onde tri-centriques du continuum électroniques et états liés." Thesis, Université de Lorraine, 2018. http://www.theses.fr/2018LORR0084/document.
This thesis is concerned by the (e,2e) simple ionization of the simplest tri-centric ion existing in nature, which is constituted by three centers forming an equilateral triangle. The electronic structure of H+3 has been largely studied during different periods in the past. Currently, it is the subject of numerous studies concerning specially its dissociative recombination with electrons, and its behavior in the field of intense LASER. The recent developments in the detection techniques has opened the possibility to realize (e,2e) simple ionization experiments where the projectile electron interacts with a gas of H+3 , and the emerging fragments are detected in coincidence. To guide these experiments, we undertake the theoretical challenge to describe this complex process, and prepare the necessary tools for the determination of the multiple differential cross section of this process. This task has needed the development and the application of an original three-center continuum wave function (ThCC), which describes the slow ejected electron in the Coulomb field of the residual tri-centric mono-electronic ion in the frame of a first order Born series procedure. Our calculations have explored the optimal conditions for the ionization process and the influence of the electron-electron correlation. Our results predict, among others, the appearance of quantum interference patterns during the variation of the multiple differential cross section with the scattering direction for a given orientation of the molecule
Selme, Marie-Odile. "Étude en liaisons fortes de la structure éléctronique des impuretés de transition et de défauts superficiels dans le titanate de strontium." Nancy 1, 1986. http://docnum.univ-lorraine.fr/public/SCD_T_1986_0329_SELME.pdf.
Khattou, Wafaa. "Contribution à l'étude théorique de la structure électronique du fer, cobalt et nickel dans les semiconducteurs II-VI." Montpellier 2, 1996. http://www.theses.fr/1996MON20270.
Kempf, Jean-Yves. "Détermination des propriétés électroniques des oxydes de métaux de transition à base de vanadium." Nancy 1, 1995. http://www.theses.fr/1995NAN10194.
Crocombette, Jean-Paul. "Approche locale de la structure électronique des oxydes de métaux de transition : étude théorique des seuils L2,3 du cation." Palaiseau, Ecole polytechnique, 1995. http://www.theses.fr/1995EPXX0045.