Dissertationen zum Thema „Anharmonicitées“
Geben Sie eine Quelle nach APA, MLA, Chicago, Harvard und anderen Zitierweisen an
Machen Sie sich mit Top-22 Dissertationen für die Forschung zum Thema "Anharmonicitées" bekannt.
Neben jedem Werk im Literaturverzeichnis ist die Option "Zur Bibliographie hinzufügen" verfügbar. Nutzen Sie sie, wird Ihre bibliographische Angabe des gewählten Werkes nach der nötigen Zitierweise (APA, MLA, Harvard, Chicago, Vancouver usw.) automatisch gestaltet.
Sie können auch den vollen Text der wissenschaftlichen Publikation im PDF-Format herunterladen und eine Online-Annotation der Arbeit lesen, wenn die relevanten Parameter in den Metadaten verfügbar sind.
Sehen Sie die Dissertationen für verschiedene Spezialgebieten durch und erstellen Sie Ihre Bibliographie auf korrekte Weise.
Chabane, Saadi. „Quasi Harmonic approximation breakdown : consequences on the thermal transport at extreme conditions“. Electronic Thesis or Diss., Sorbonne université, 2024. https://accesdistant.sorbonne-universite.fr/login?url=https://theses-intra.sorbonne-universite.fr/2024SORUS297.pdf.
Der volle Inhalt der QuelleThe lattice dynamics and vibrational properties of materials are typically well described by a harmonic model at low and moderate temperatures, where phonons are assumed to behave independently. However, at high temperatures, this assumption fails as phonon interactions become significant. Understanding these anharmonic interactions between lattice modes is crucial for both fundamental research and practical applications, as they significantly influence physical properties such as thermal transport and elastic properties.Thermal conductivity of the minerals constituting planetary interiors plays a key role in controlling heat transfer within planets, thereby influencing planetary dynamics and thermo-chemical history (Samuel et al., 2021). The heat flux from the core to the mantle directly impacts the degree of basal heating of the mantle, the rate of core cooling, and inner core growth, which in turn affect outer core dynamics and magnetic field generation and evolution. Thus, understanding phonon interactions provides insights into Earth's history and evolution.The aim of this thesis is to investigate the behavior of anharmonic terms at the extreme temperature and pressure conditions of Earth's lower mantle, focusing on Magnesium Oxide (MgO) which is an end-member for ferropericlase (Mg,Fe)O that constitutes 20% of the mantle's volume. This study employs Density Functional Theory (DFT) based methods, specifically Density Functional Perturbation Theory (DFPT) and the Stochastic Self-Consistent Harmonic Approximation (SSCHA). These methodologies allow access to anharmonicity up to the fourth-order (four-phonon interactions). The results will be benchmarked against Inelastic X-ray Scattering (IXS) and Infra-Red spectroscopy (IR) measurements conducted in our group at varying temperatures.Subsequently, we will discuss the thermal conductivity (TC) obtained through the Boltzmann transport equation as a function of temperature, emphasizing the importance of considering defects in the analysis of TC. We then explore the extreme conditions of Earth's lower mantle, with temperatures of thousands of Kelvin and pressures at the Mbar scale, to identify the behavior of anharmonicity in MgO throughout this region. Our theoretical treatment elucidates the microscopic origin of the observed drop in TC at the bottom of the lower mantle, attributed to the interplay between three- and four-phonon interactions and emphasizes on the importance of presence of defects on lattice thermal conductivity even at extreme T and P conditions
Ridou, Colette. „Anharmonicité et transitions de phase par rotations d'octaèdres dans les pérovskites AMX3“. Grenoble : ANRT, 1985. http://catalogue.bnf.fr/ark:/12148/cb37595127k.
Der volle Inhalt der QuelleBasire, Marie. „Anharmonicité et spectroscopie IR de systèmes moléculaires complexes : application aux hydrocarbures aromatiques polycycliques“. Paris 11, 2010. http://www.theses.fr/2010PA112195.
Der volle Inhalt der QuelleThe subject of my thesis concerns a theoretical treatment of Infra-Red (IR) spectroscopy of complex molecular systems. L have focussed in particular on Polycyclic Aromatic Hydrocarbons (PAHs). These molecules are known to be present in the InterStellar Medium (ISM) on the basis of their spectral signature in the IR region. The objective of my thesis is to probe the anharmonicity of the potential energy surface of the molecular ground states and the effect on the spectral profiles. The simulated spectra are compared to experimental measurements or observations to determine if isolated PAHs exist in the ISM. The first step was to simulate the absorption and emission spectra within the microcanonical ensemble using a multicanonical Monte Carlo procedure. In order to achieve this, l had to develop an original method based on the Wang-Landau algorithm which allows a quantum anharmonic calculation of the rovibrational density of states. For a given temperature, the IR absorption spectra of a molecule can be calculated relatively simply, and the evolution of any particular spectral profile of the different rovibrational bands can be easily studied as a function of the internaI temperature of the molecule. The emission spectra generated by an IR cascade in the electronic ground state can also be simulated by a kinetic Monte Carlo process. The same theoretical scheme has enabled the multiphotonic absorption spectra of the PAHs to be compared with the absorption spectra. Finally, the PAH IR absorption spectra as a function of temperature were also simulated using ab-initio molecular dynamics calculations (Car-Parrinello method)
Fallot, Muriel. „Recherche de l'état à trois phonons dans le 40Ca“. Paris 6, 2002. https://tel.archives-ouvertes.fr/tel-00002925.
Der volle Inhalt der QuelleProville, Laurent. „Modélisations numériques en physique des matériaux“. Habilitation à diriger des recherches, Université Paul Cézanne - Aix-Marseille III, 2004. http://tel.archives-ouvertes.fr/tel-00336021.
Der volle Inhalt der QuelleLes calculs réalisés à l'échelle atomique (dynamique moléculaire, Monte Carlo cinétique et résolution de l'équation de Schrödinger) nous ont également permis de traiter différentes problématiques fondamentales en physique et chimie des matériaux: le glissement des dislocations en solution solide, la cinétique de dépôt sur surfaces ainsi que le spectre de vibration de cristaux moléculaires. Une présentation des principaux résultats aura lieu en salle de thèse de la Faculté de St-Jérôme, Mercredi 22 decembre à 14H.
Haro, Poniatowski Emmanuel. „Étude expérimentale et théorique de l'anharmonicité dans le silicium“. Paris 6, 1986. http://www.theses.fr/1986PA066066.
Der volle Inhalt der QuelleMarronnier, Arthur. „Anharmonicity and Instabilities in Halide Perovskites for Last Generation Solar Cells“. Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLX031/document.
Der volle Inhalt der QuelleHybrid halide perovskites (ABX3) have emerged over the past five years as absorber layers for novel high-efficiency low-cost solar cells combining the advantages of organic (molecule A) and inorganic (metal B, halogen X) materials. Very recently, fully inorganic perovskite quantum dots also shown promising efficiencies, making them a potentially stable and efficient alternative to their hybrid cousins.The aim of this PhD thesis is to study and better understand both the structural and thermodynamic instabilities of these halide perovskites, with a specific focus on purely inorganic CsPbI3 structures.We first use various ab-initio techniques, the majority of which are based on Density Functional Theory (DFT) and its linear-response approach (DFPT), to investigate the vibrational and electronic properties of the different phases of CsPbI3. While the black γ-phase, crucial for photovoltaic applications, is shown to behave harmonically around equilibrium, for the other three phases frozen phonon calculations reveal a Brillouin zone center double-well instability. We also show that avoiding the order-disorder entropy term arising from these double-well instabilities is key in order to prevent the formation of the yellow perovskitoid phase, and evidence a Rashba effect when using the symmetry breaking structures obtained through frozen phonon calculations. We then analyze the structural changes and the dynamical Rashba splitting along molecular dynamics trajectories in the light of our findings.In a second phase, we investigate the thermodynamical stability of hybrid perovskite MAPbI3. Our experimental ellipsometry-based study brings better understanding of the chemical decomposition of MAPbI3 into its two precursors, methylammonium and lead iodides, which we predicted using DFT stability diagram calculations and which we confirm by X-Ray diffraction. Last, we prove that hybrid perovskite structure MAPbI3 behaves more like inorganic compounds (high dielectric constant, low exciton binding energy) than like organic materials (low dielectric constant, high exciton binding energy)
Andrea, Luc. „Modélisation du transport thermique dans des matériaux thermoélectriques“. Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066122/document.
Der volle Inhalt der QuelleThermoelectric materials provide a way to convert thermal energy into electrical energy. Nonetheless, their low efficiency is the main obstacle for global scale applications. Experimentally, specific treatments can lead to great improvement in the efficiency, mainly by lowering the thermal conductivity. This thesis is aimed at calculating from first principles, the thermal transport properties in perfect and doped half-Heusler thermoelectric materials. We begin with a theoretical analysis of the harmonic and anharmonic properties of phonons for perfect phases.The density functional theory is used to deduce the phonons lifetime from phonon-phonon interactions. The lifetimes are integrated into the Boltzmann transport equation for the phonon density, which solution allows us to compute fully ab initio the lattice thermal conductivity. The purpose of point defects is to scatter the phonons and thus reduce thermal conductivity. We developed two methods to account for the defects on thermal transport. The first one, based on a mean field approach, is suitable for the high concentration regimes. The second one in the framework of Green functions theory is used for dilute regimes. Both methods consistently show that the main reduction of thermal conductivity is already obtained within around 10 % of solute elements in NiTiSn, NiZrSn and NiHfSn
Herbane, Mustapha Saïd. „Piégeage et refroidissement laser d'ions calcium pour un étalon de fréquence optique“. Aix-Marseille 1, 2002. http://www.theses.fr/2002AIX11008.
Der volle Inhalt der QuelleLe, Cleac'H A. „Contribution à l'étude des propriétés physiques des minéraux à haute pression : Spectroscopie et calcul des grandeurs thermodynamiques de la lawsonite, des épidotes et des polymorphes de Si02“. Phd thesis, Université Rennes 1, 1989. http://tel.archives-ouvertes.fr/tel-00655926.
Der volle Inhalt der QuelleAlmeida, Silva Ribeiro Guilherme. „Strong anharmonicity in the phonon spectra of PbTe and SnTe evaluated via the stochastic self-consistent harmonic approximation“. Thesis, Paris 6, 2017. http://www.theses.fr/2017PA066737.
Der volle Inhalt der QuelleAt room temperature, PbTe and SnTe are efficient thermoelectrics with a cubic structure. At low temperature, snte undergoes a ferroelectric transition with a critical temperature strongly dependent on the hole concentration, while PbTe is an incipient ferroelectric. In this thesis by using the stochastic self-consistent harmonic approximation, we investigate the anharmonic phonon spectra and the occurrence of a ferroelectric transition in both systems. We find that vibrational spectra strongly depends on the approximation used for the exchange-correlation kernel in density functional theory. If gradient corrections and the theoretical volume are employed, then the calculation of the free energy hessian leads to phonon spectra in good agreement with experimental data for both systems. In PbTe, we reproduce the transverse optical mode phonon satellite detected in inelastic neutron scattering and the crossing between the transverse optical and the longitudinal acoustic modes along the gamma-x direction. In the case of SnTe, we describe the occurrence of a ferroelectric transition from the high temperature fm3m Structure to the low temperature r3m one
Labeguerie, Pierre. „Modélisation du champ électrique interne d'un solide:application à la détermination des propriétés dérivées de la polarisation. Calcul du spectre de phonon“. Phd thesis, Université de Pau et des Pays de l'Adour, 2005. http://tel.archives-ouvertes.fr/tel-00264922.
Der volle Inhalt der QuelleAndrea, Luc. „Modélisation du transport thermique dans des matériaux thermoélectriques“. Electronic Thesis or Diss., Paris 6, 2016. http://www.theses.fr/2016PA066122.
Der volle Inhalt der QuelleThermoelectric materials provide a way to convert thermal energy into electrical energy. Nonetheless, their low efficiency is the main obstacle for global scale applications. Experimentally, specific treatments can lead to great improvement in the efficiency, mainly by lowering the thermal conductivity. This thesis is aimed at calculating from first principles, the thermal transport properties in perfect and doped half-Heusler thermoelectric materials. We begin with a theoretical analysis of the harmonic and anharmonic properties of phonons for perfect phases.The density functional theory is used to deduce the phonons lifetime from phonon-phonon interactions. The lifetimes are integrated into the Boltzmann transport equation for the phonon density, which solution allows us to compute fully ab initio the lattice thermal conductivity. The purpose of point defects is to scatter the phonons and thus reduce thermal conductivity. We developed two methods to account for the defects on thermal transport. The first one, based on a mean field approach, is suitable for the high concentration regimes. The second one in the framework of Green functions theory is used for dilute regimes. Both methods consistently show that the main reduction of thermal conductivity is already obtained within around 10 % of solute elements in NiTiSn, NiZrSn and NiHfSn
Ayrinhac, Simon. „Propagation et atténuation du son dans la silice - étude par spectroscopie Brillouin et acoustique picoseconde“. Phd thesis, Université Montpellier II - Sciences et Techniques du Languedoc, 2008. http://tel.archives-ouvertes.fr/tel-00626302.
Der volle Inhalt der QuelleSanejouand, Yves-Henri. „Les modes normaux de basse fréquence des protéines“. Habilitation à diriger des recherches, Université Claude Bernard - Lyon I, 2007. http://tel.archives-ouvertes.fr/tel-00258781.
Der volle Inhalt der QuelleFARHI, Emmanuel. „Etude des anomalies paraelectriques quantiques de perovskites derivees de KTaO_3“. Phd thesis, Université Montpellier II - Sciences et Techniques du Languedoc, 1998. http://tel.archives-ouvertes.fr/tel-00003038.
Der volle Inhalt der Quelledi'electriques qui devraient ?etre ferro'electriques
en dessous de la temp'erature de CurieWeiss Tc .
Que se passetil ? A basse temp'erature, les
fluctuations ferro'electriques sont contr?ol'ees par
un mode de vibration transverse optique (TO),
dit ferro'electrique qui devient mou (sa fr'equence
diminue) au centre de la zone de Brillouin lorsque
la temp'erature d'ecro?it. Mais pour T ! T q ¸ Tc ,
le fort mouvement quantique de point z'ero de l'ion
central (Ta dans KTaO3) emp?eche la condensation
du mode ferro'electrique, dont la fr'equence se sta
bilise `a basse 'energie. La constante di'electrique
ffl sature `a une tr`es grande valeur, et un fort cou
plage avec le mode transverse acoustique devient
visible.
En 1991, K.A. M¨uller, d'apr`es une 'etude RPE,
envisage une transition de phase d'un nouveau
type dans ces mat'eriaux. B. Hehlen et E.
Courtens s'int'eressent alors aux propri'et'es basses
fr'equences du SrTiO3 et du KTaO3 . Les 'etudes
de diffusion neutronique, mais surtout Brillouin,
montrent alors, parmi les nombreuses anomalies,
une nouvelle excitation tr`es basse fr'equence, qu'ils
attribuent au second son, la propagation ondula
toire de la chaleur.
Ce travail pr'esente des r'esultats originaux
obtenus en diffusion neutronique et Brillouin `a
basse temp'erature (5300 K). Une param'etrisation
des nappes de phonons dans KTaO3 a servi de
base au calcul de la largeur normale des phonons,
de la vitesse th'eorique du second son, dans le cas
o`u il serait effectivement observable, et du spectre
complet de diffusion Brillouin par des processus de
diff'erence de deux phonons. La comparaison des
simulations avec l'exp'erience montre un bon ac
cord pour le calcul des largeurs et des nappes, et le
processus physique observ'e en spectroscopie Bril
louin est probablement celui de diff'erence de deux
phonons. Les diff'erents aspects de la dynamique
des phonons basse fr'equence peuvent ?etre unifi'es
au sein d'une th'eorie de diffusion Brillouin au sec
ond ordre.
Mots clefs : phonons, para'electriques quan
tiques, second son, anharmonicit'e, diffusion neu
tronique, spectroscopie Brillouin, mod'elisation et
simulation num'erique, KTaO3 , SrTiO3 .
Attal, Loïse. „A system-bath model to address anharmonicity effects in the quantum vibrational dynamics of complex or interacting molecular systems“. Electronic Thesis or Diss., université Paris-Saclay, 2024. http://www.theses.fr/2024UPASP129.
Der volle Inhalt der QuelleQuantum dynamics allows for the most complete description of the time evolution of molecular systems by accounting for their quantized nature. Yet, in practice, the effort to solve the underlying equations grows exponentially with the number of degrees of freedom. This is the so-called curse of dimensionality. It is particularly striking for open quantum systems (those in contact with an environment), which are ubiquitous in physics and chemistry. It also considerably limits our ability to rigorously describe molecules containing more than a few atoms. In that context, the aim of this project is to better understand interactions occurring both inside complex molecular systems and between small molecules and their environment. The main project in my Ph.D. thesis consisted of the development and implementation of a new, homemade, system-bath model for the vibrational quantum dynamics of intermediate to large-size molecular systems. This model, which we named the Effective Bath State (EBS) model, consists of a one-dimensional anharmonic system interacting with a finite but large-dimensional harmonic environment (the bath). In a molecular context, the system consists of one vibrational normal mode that is considered to be of particular interest, while the remaining vibrational modes are part of the bath. The EBS model can also be used in a more general context where the one-dimensional system is an effective mode representing the molecule, and the bath represents a finite-dimension environment such as a cluster, a quantum dot, or another nanoscale device. In the EBS approach, the bath is coarse-grained into effective energy states (EESs) that are defined based on the total bath energy. The effective states interact with the system through a rigorous calculation that accounts for the number of accessible microstates within the EESs involved in each transition. This procedure uses probabilities obtained from microcanonical statistics, thus assuming fast energy redistribution inside the bath. As the bath is explicitly represented and made of a finite number of harmonic oscillators, it can account for non-Markovian effects in the system-bath interaction. In the context of finite molecular systems, it can describe vibrational recurrences. The EBS approach strongly reduces the effective dimension of the bath and the way it increases with the number of degrees of freedom while keeping information about the global state of the bath and its evolution with time. Using EESs also makes quantum dynamics at finite bath energy and temperature more accessible by strongly reducing its computational cost
Sanejouand, Yves-Henri. „Etude théorique des mouvements internes de grande amplitude de la décaalanine et du fragment C-terminal de la protéine ribosomale L7/L12“. Phd thesis, Université Paris Sud - Paris XI, 1990. http://tel.archives-ouvertes.fr/tel-00266537.
Der volle Inhalt der QuelleAkkermans, Éric. „Propagation d'ondes dans les milieux désordonnés“. Grenoble 1, 1986. http://www.theses.fr/1986GRE10050.
Der volle Inhalt der QuelleNGUYEN-THI, Van-Oanh. „SPECTROSCOPIE ET STABILITE DES HYDROCARBURES AROMATIQUES POLYCYCLIQUES DANS LES CONDITIONS DU MILIEU INTERSTELLAIRE“. Phd thesis, Université Paris Sud - Paris XI, 2003. http://tel.archives-ouvertes.fr/tel-00005244.
Der volle Inhalt der QuellePIMENTA, MARCOS ASSUNCAO. „Transitions de phase a haute temperature et conduction ionique dans likso:(4) et composes apparentes“. Orléans, 1987. http://www.theses.fr/1987ORLE2045.
Der volle Inhalt der QuelleJoshi, Prakriti Pradhan. „Contributions of Lattice Anharmonicities to Optoelectronic Properties of Lead Halide Perovskites“. Thesis, 2019. https://doi.org/10.7916/d8-ebca-bq21.
Der volle Inhalt der Quelle