Auswahl der wissenschaftlichen Literatur zum Thema „Many-Body formalisms“
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Zeitschriftenartikel zum Thema "Many-Body formalisms"
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Faber, C., P. Boulanger, C. Attaccalite, I. Duchemin und X. Blase. „Excited states properties of organic molecules: from density functional theory to the GW and Bethe–Salpeter Green's function formalisms“. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 372, Nr. 2011 (13.03.2014): 20130271. http://dx.doi.org/10.1098/rsta.2013.0271.
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Many-body Green's function perturbation theories, such as the GW and Bethe–Salpeter formalisms, are starting to be routinely applied to study charged and neutral electronic excitations in molecular organic systems relevant to applications in photovoltaics, photochemistry or biology. In parallel, density functional theory and its time-dependent extensions significantly progressed along the line of range-separated hybrid functionals within the generalized Kohn–Sham formalism designed to provide correct excitation energies. We give an overview and compare these approaches with examples drawn from the study of gas phase organic systems such as fullerenes, porphyrins, bacteriochlorophylls or nucleobases molecules. The perspectives and challenges that many-body perturbation theory is facing, such as the role of self-consistency, the calculation of forces and potential energy surfaces in the excited states, or the development of embedding techniques specific to the GW and Bethe–Salpeter equation formalisms, are outlined.
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AL-SUGHEIR, M. K., H. B. GHASSIB und B. R. JOUDEH. „FERMI PAIRING IN DILUTE 3He-HeII MIXTURES“. International Journal of Modern Physics B 20, Nr. 18 (20.07.2006): 2491–504. http://dx.doi.org/10.1142/s0217979206034844.
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In this paper the Galitskii–Migdal–Feynman (GMF) formalism is applied to dilute 3He-HeII mixtures. In particular, the effect of the hole-hole scattering on pairing in these systems is investigated. To this end, the relative phase shifts incorporating many-body effects based on both Brueckner–Bethe–Goldstone (BBG) and GMF formalisms are calculated. In the GMF formalism, the S-wave phase shift at zero relative momentum is –π and has a cusp at the Fermi momentum; while in the BBG formalism, this phase shift has zero values up to the Fermi momentum. From these results we conclude that hole-hole scattering plays a crucial role in any possible fermion-fermion pairing in these systems.
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Evangelista, Francesco A. „Automatic derivation of many-body theories based on general Fermi vacua“. Journal of Chemical Physics 157, Nr. 6 (14.08.2022): 064111. http://dx.doi.org/10.1063/5.0097858.
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This paper describes Wick&d, an implementation of the algebra of second-quantized operators normal ordered with respect to general correlated references and the corresponding Wick theorem [D. Mukherjee, Chem. Phys. Lett. 274, 561 (1997) and W. Kutzelnigg and D. Mukherjee, J. Chem. Phys. 107, 432 (1997)]. Wick&d employs a compact representation of operators and a backtracking algorithm to efficiently evaluate Wick contractions. Since Wick&d can handle both fully and partially contracted terms, it can be applied to both projective and Fock-space many-body formalisms. To demonstrate the usefulness of Wick&d, we use it to evaluate the single-reference coupled cluster equations up to octuple excitations and report an automated derivation and implementation of the second-order driven similarity renormalization group multireference perturbation theory.
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HU, BEN YU-KUANG. „MANY-BODY EFFECTS IN FRICTIONAL DRAG BETWEEN COUPLED TWO-DIMENSIONAL ELECTRON SYSTEMS“. International Journal of Modern Physics B 13, Nr. 05n06 (10.03.1999): 469–78. http://dx.doi.org/10.1142/s0217979299000369.
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Independently contacted coupled quantum wells separated by barriers which allow significant interlayer interactions but no tunneling have been fabricated. When current is passed through one layer, the interlayer interactions drag carriers in the second layer, resulting in a voltage response (for open circuits). The magnitude of the response gives a quantitative measure of the effective interlayer interactions and response functions of the system, and hence this is an excellent laboratory for the study of many-body phenomena in two-dimensional electron gases. We review the Boltzmann and Kubo formalisms for the theory of drag effects in coupled quantum wells and discuss three specific cases where many-body effects significantly affect the drag: (1) acoustic phonon-mediated drag, (2) large enhancements due to coupled plasmon modes, and (3) interplay of screening and Landau levels in large magnetic fields.
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Lindgren, I., S. Salomonson und D. Hedendahl. „Many-body-QED perturbation theory: Connection to the two-electron BetheSalpeter equation“. Canadian Journal of Physics 83, Nr. 3 (01.03.2005): 183–218. http://dx.doi.org/10.1139/p05-027.
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The connection between many-body perturbation theory (MBPT) and quantum electrodynamics (QED) is reviewed for systems of two fermions in an external field. The treatment is mainly based on the recently developed covariant-evolution-operator method for QED calculations (I. Lindgren, S. Salomonson, and B. Åsén. Phys. Rep. 389, 161 (2004)), which is quite similar in structure to MBPT. At the same time, this procedure is closely related to the S-matrix and Green's-function formalisms and can therefore serve as a bridge connecting various approaches. It is demonstrated that the MBPTQED scheme, when carried to all orders, leads to a Schrödinger-like equation, equivalent to the BetheSalpeter (BS) equation. A Bloch equation in commutator form that can be used for an "extended" or quasi-degenerate model space is derived. This is a multi-state equation that has the same relation to the single-state BS equation as the standard Bloch equation has to the ordinary Schrödinger equation. It can be used to generate a perturbation expansion compatible with the BS equation even in the case of a quasi-degenerate model PACS Nos.: 01.65.+g, 02.60.Cb, 03.65.Pm, 31.10+z, 31.15Md, 31.30Jv
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Chaudhuri, Rajat, Dhiman Sinha und Debashis Mukherjee. „On the extensivity of the roots of effective Hamiltonians in many-body formalisms employing incomplete model spaces“. Chemical Physics Letters 163, Nr. 2-3 (November 1989): 165–70. http://dx.doi.org/10.1016/0009-2614(89)80029-6.
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Bauman, Nicholas P., Eric J. Bylaska, Sriram Krishnamoorthy, Guang Hao Low, Nathan Wiebe, Christopher E. Granade, Martin Roetteler, Matthias Troyer und Karol Kowalski. „Downfolding of many-body Hamiltonians using active-space models: Extension of the sub-system embedding sub-algebras approach to unitary coupled cluster formalisms“. Journal of Chemical Physics 151, Nr. 1 (07.07.2019): 014107. http://dx.doi.org/10.1063/1.5094643.
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Alastuey, A. „Statistical Mechanics of Quantum Plasmas Path Integral Formalism“. International Astronomical Union Colloquium 147 (1994): 43–77. http://dx.doi.org/10.1017/s0252921100026312.
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AbstractIn this review, we consider a quantum Coulomb fluid made of charged point particles (typically electrons and nuclei). We describe various formalisms which start from the first principles of statistical mechanics. These methods allow systematic calculations of the equilibrium quantities in some particular limits. The effective-potential method is evocated first, as well as its application to the derivation of low-density expansions. We also sketch the basic outlines of the standard many-body perturbation theory. This approach is well suited for calculating expansions at high density (for Fermions) or at high temperature. Eventually, we present the Feynman-Kac path integral representation which leads to the introduction of an auxiliary classical system made of extended objects, i.e., filaments (also called “polymers”). The familiar Abe-Meeron diagrammatic series are then generalized in the framework of this representation. The truncations of the corresponding virial-like expansions provide equations of state which are asymptotically exact in the low-density limit at fixed temperature. The usefulness of such equations for describing the inner regions of the sun is briefly illustrated.
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Villani, Matteo, und Xavier Oriols. „Can Wigner distribution functions with collisions satisfy complete positivity and energy conservation?“ Journal of Computational Electronics 20, Nr. 6 (23.11.2021): 2232–44. http://dx.doi.org/10.1007/s10825-021-01798-1.
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AbstractTo avoid the computational burden of many-body quantum simulation, the interaction of an electron with a photon (phonon) is typically accounted for by disregarding the explicit simulation of the photon (phonon) degree of freedom and just modeling its effect on the electron dynamics. For quantum models developed from the (reduced) density matrix or its Wigner–Weyl transformation, the modeling of collisions may violate complete positivity (precluding the typical probabilistic interpretation). In this paper, we show that such quantum transport models can also strongly violate the energy conservation in the electron–photon (electron–phonon) interactions. After comparing collisions models to exact results for an electron interacting with a photon, we conclude that there is no fundamental restriction that prevents a collision model developed within the (reduced) density matrix or Wigner formalisms to satisfy simultaneously complete positivity and energy conservation. However, at the practical level, the development of such satisfactory collision model seems very complicated. Collision models with an explicit knowledge of the microscopic state ascribed to each electron seems recommendable (Bohmian conditional wavefunction), since they allow to model collisions of each electron individually in a controlled way satisfying both complete positivity and energy conservation.
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Baer, Roi, und Daniel Neuhauser. „Many-body scattering formalism of quantum molecular conductance“. Chemical Physics Letters 374, Nr. 5-6 (Juni 2003): 459–63. http://dx.doi.org/10.1016/s0009-2614(03)00709-7.
Der volle Inhalt der QuelleDissertationen zum Thema "Many-Body formalisms"
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Amblard, David. „Formalisme à N-corps GW environné dans une approche fragment : développements et applications à des systèmes complexes“. Electronic Thesis or Diss., Université Grenoble Alpes, 2024. http://www.theses.fr/2024GRALY028.
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Le formalisme GW, dans le cadre des théories de perturbation à N-corps utilisant les fonctions de Green, gagne en popularité pour la description des propriétés électroniques des systèmes de la matière condensée en physique du solide, et plus récemment en chimie. Son application à des systèmes complexes d'intérêt en nanoscience, chimie, voire biologie, est freinée cependant par son coût numérique en particulier dans le cas de systèmes désordonnés, ou immergés dans un environnement ouvert (un solvant, un milieu moléculaire, une électrode, etc.) Le but de cette thèse est de développer des techniques multi-échelles, combinant des approches à N-corps de haut niveau pour le sous-système d'intérêt, avec une description simplifiée, mais tout de même totalement ab initio, d'un environnement électrostatique et diélectrique. Ces approches vont donc au-delà des modèles classiques paramétrés, développés en particulier dans la communauté chimie quantique, et basés sur une description continue (« polarizable continuum model ») ou discrète (QM/MM) de l’environnement.Pour atteindre cet objectif, nous adoptons une approche en fragments de l'environnement, particulièrement adaptée aux systèmes moléculaires. La susceptibilité électronique non-interagissante devient ainsi diagonale par blocs, permettant d'abaisser la complexité algorithmique de quartique à cubique. Pour réduire le pré-facteur associé à l’obtention du potentiel écranté W (équation de Dyson), nous avons développé un algorithme de compression de l’opérateur susceptibilité. L’obtention automatique d’une base de polarisation très compacte permet de réduire fortement la taille des blocs de susceptibilité associés aux fragments de l'environnement. Cette méthode permet de calculer la réponse diélectrique de systèmes contenant des centaines de milliers d'atomes avec une excellente précision. Cette approche est présentée via l'étude de cristaux de fullerènes en volume, en surface, et en sous-surface.Alors que le formalisme GW est dynamique par nature, avec ainsi un potentiel coulombien écranté W dépendant de la fréquence, une première étude est réalisée dans le cadre d'une approximation statique (limite basse fréquence) pour décrire l’écrantage par l’environnement. Une telle approche s'inscrit dans la continuité des modèles semi-empiriques traditionnels pour la description d’un milieu environnant polarisable. Cette thèse est donc l'occasion de mesurer la validité d'une telle approximation, qui suppose que l’environnement répond de façon instantanée à une excitation électronique, grâce à une comparaison explicite avec une description totalement dynamique de la réponse diélectrique de l'environnement. L'étude d'une surface de fullerènes, ainsi que d'une molécule d'eau dans un nanotube de carbone métallique, montrent qu'une description statique de l'environnement induit des erreurs sur l'énergie de polarisation inférieure à 10% sous condition que le « repliement » de l’environnement soit correctement effectué.L'approche fragment est également appliquée à des cristaux covalents isolants, et en particulier au nitrure de bore hexagonal (h-BN). Nous avons illustré en particulier comment calculer les niveaux d’énergie de défauts ponctuels dans h-BN, dans la vraie limite diluée, et donnons les lois d’échelle pour la renormalisation de ces niveaux de la monocouche vers un nombre (n) de couches. Cette étude démontre qu’à l’instar des systèmes moléculaires, la fragmentation de systèmes covalents isolants est possible, en lien sans doute avec le caractère très courte portée de la susceptibilité dans ces systèmes.Ces développements, permettant l’extension d’approches quantiques à N-corps à des systèmes de plus en plus complexes, ont été implémentés dans le code beDeft, un code massivement parallèle pour l’étude des propriétés électroniques de systèmes de grande tailleThe GW formalism, a Green’s function many-body perturbation theory, is growing in popularity for the description of the electronic properties of condensed matter systems in solid-state physics, and more recently chemistry. Unfortunately, its application to complex systems of interest in nanosciences, chemistry, or even biology, is hampered by the large associated computing cost, in particular in the case of disordered systems, or systems immersed in an opened environment (a solvent, a molecular medium, an electrode, etc.) The goal of the present PhD thesis is to focus on the development of multiscale techniques, merging high-level many-body treatments of the subsystem of interest, with a simplified but fully ab initio description of the electrostatic and dielectric environment. Such approaches aim to go beyond classical parametrized models, mainly developed in the quantum chemistry community, which are based on a continuum (“polarizable continuum model”) or discrete (QM/MM) description of the environment.To reach such a goal, we adopt a divide-and-conquer fragmentation scheme for the environment, particularly suited to molecular systems. This leads to a block-diagonal non- interacting electron susceptibility, decreasing the algorithmic complexity from quartic to cubic. To reduce the prefactor associated with the inversion of the Dyson equation for the screened Coulomb potential W, we have further developed a compression algorithm for the susceptibility operator. The automatic computation of an extremely compact polarization basis set allows a large reduction of the size of the susceptibility blocks, associated to the fragments in the environment. Such a method enables us to compute the dielectric response of systems made of several hundred thousand atoms, with an excellent accuracy when it comes to reproduce the effect of the environment as a response to an excitation in the immersed subsystem. This approach is presented through the study of fullerene bulk, surface and subsurface crystals.While the GW formalism is dynamical, with a frequency-dependent screened Coulomb potential W, a first study is done adopting a static approximation (low-frequency limit) for the screening properties of the environment. Such an approach follows the traditional semi-empirical models of a polarizable environment. This PhD thesis assesses the validity of such an approximation, which assumes an instantaneous response (adiabatic limit) of the environment to an electronic excitation, thanks to an explicit comparison with a fully dynamical dielectric response of the environment. The study of a surface of fullerenes, as well as a water molecule inside a metallic carbon nanotube, show that a static description of the environment leads to errors on the polarization energy below 10%, provided that the “folding” of the environment is treated in a proper way.The fragment approach is also applied to covalent insulator crystals, and more particularly to hexagonal boron nitride (h-BN). We explain how to compute the energy levels of point defects in h-BN, in the true dilute limit, and we give the asymptotic scaling laws for the renormalization of these energy levels, from the monolayer to a (n)-layer system. This study highlights thus the possibility to apply the fragment approach to covalent insulator systems, a possibility hinging probably on the short range behavior of the susceptibility in these systems.All of these developments, extending ab initio many-body methods to increasingly complex systems, have been implemented in the massively parallel code beDeft, dedicated to the study of the electronic properties of large scale systems
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Hickel, Tilmann. „Theory of many-body effects in the Kondo-lattice model“. Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2006. http://dx.doi.org/10.18452/15500.
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Das magnetische Verhalten zahlreicher Materialien lässt sich auf eine indirekte Wechselwirkung lokalisierter magnetischer Momente, vermittelt durch die Elektronen eines Leitungsbandes, zurückführen. Das Kondo-Gitter-Modell hat sich als elegante Möglichkeit bewährt, diesen Prozess quantenmechanisch zu beschreiben. Es reduziert die Physik auf eine intraatomare Wechselwirkung der Spins von lokalisierten und itineranten Elektronen. Die vorliegende Arbeit ist den analytischen Eigenschaften dieses Modells gewidmet. Die besondere Herausforderung des Kondo-Gitter-Modells besteht dabei im Zusammenwirken zweier verschiedener Teilchensorten, beschrieben durch Fermi-Operatoren sowie quantenmechanische Spins. Bisherige Untersuchungen haben sich in der Regel nur auf eine der beiden Teilchensorten konzentriert. Mit der Projektions-Operator-Methode stellen wir eine Möglichkeit vor, beide Teilsysteme in gleicher Qualität zu behandeln. Die Auswertung des Teilsystems der itineranten Elektronen führt auf einen Ausdruck für die Selbstenergie, der lineare und quadratische Effekte in der Wechselwirkung exakt beschreibt. Die resultierenden Zustandsdichten weisen starke Korrelationseffekte auf. Deren Untersuchung dient sowohl der Bestätigung von Ergebnissen weniger systematischer Zugänge als auch dem Aufzeigen neuer Vielteilchen-Phänomene. Die Anwendung der Projektions-Operator-Methode auf das System der lokalisierten Momente führt zu einer Analyse der bereits bekannten RPA (random phase approximation). Zu diesem Zweck werden die Magnonenspektren und die Curie-Temperaturen systematisch untersucht. Dabei treten bisher unbekannte Schwachpunkte der RPA zu Tage, die auch die Kombination mit Theorien für das itinerante Teilsystem verhindern. Verbesserungen und Alternativen zur RPA werden diskutiert.The magnetic behaviour of various materials is due to an indirect interaction of localized magnetic moments, which is based on itinerant electrons in a conduction band. The Kondo-lattice model is an elegant approach for a quantum-mechanical description of this process. It reduces the relevant physics to an intra-atomic exchange interaction of the localized and the itinerant electrons. The aim of the present work is a detailed investigation of analytic properties of this model. Here, the interplay of two distinct types of particles, described by Fermi operators and quantum-mechanical spin operators respectively, is a major challenge of the considered model. Previous studies have focused on one of these subsystems only. Using the projection-operator method, we suggest an efficient way to describe both subsystems on the same level of approximation. An evaluation of the subsystem of itinerant electrons yields an expression for the self-energy, which describes linear and quadratic interaction effects exactly. The densities of states derived with this theory show strong correlation effects. We were able to assess results obtained with less systematic approaches and to predict new many-particle effects. The application of the projection-operator method to the subsystem of localized magnetic moments results in a detailed analysis of the RPA (random phase approximation). The dependence of magnon spectra and Curie temperatures on model parameters are investigated systematically. Previously unknown drawbacks of the RPA are revealed, which prevent the combination of these results with theories for the itinerant subsystem. Improvements beyond RPA and alternative approximations are discussed.
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Morinière, Maxime. „Formalismes et méthodes pour le calcul de la réponse linéaire des systèmes isolés“. Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAY096/document.
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La réponse linéaire de la théorie de la fonctionnelle de la densité dépendante du temps est étudiée dans le cadre du formalisme d'ondelettes du code BigDFT, qui permet d'exprimer les fonctions d'onde électroniques sur une grille de simulation dans l'espace réel. L'objectif est de déterminer un spectre d'excitations de référence pour un système et un potentiel d'échange-corrélation donnés.Il apparaît que seule une partie du spectre, concernant les transitions entre orbitales liées, peut être facilement amenée à convergence par rapport aux paramètres d'entrée de BigDFT, que sont l'extension de la grille de simulation et le nombre d'orbitales du continuum qui sont considérées pour le calcul des spectres. L'énergie de la dernière orbitale inoccupée utilisée dans les calculs se révèle d'ailleurs être un paramètre plus important que ce nombre d'orbitales inoccupées. La justification vient de l'étude de la complétude des bases formées par les orbitales de l'état fondamental du système. Tout ceci permet de porter un regard neuf sur les résultats obtenus avec le formalisme à base gaussienne, tel qu'implémenté dans le code NWChem.En ce qui concerne la convergence du spectre de plus haute énergie, concernant des transitions entre orbitales occupées et orbitales inoccupées du continuum, l'espoir d'une convergence se heurte au problème du tassement du continuum. Il faut alors songer à une manière différente de capter l'information contenue dans ce continuum.Le formalisme des états résonants, dont les fondements ont été posés lors de la première moitié du XXème siècle, est une piste très encourageante pour cela. Une étude préliminaire dans le cas du puits de potentiel carré à une dimension est donc présentée. La première étape a consisté en la détermination de ces états résonants, dont les énergies et fonctions d'onde sont complexes. Une normalisation a notamment pu leur être attribuée. Il est ensuite montré, sous certaines conditions, que la base formée par les états propres de ce potentiel, dont une partie est constituée par les états du continuum, peut être efficacement remplacée par une base discrète et complète faite d'états résonants. Des applications numériques montreront qu'ils peuvent être avantageusement utilisés pour définir la fonction de Green ou encore calculer la propagation temporelle d'un paquet d'ondeThe linear response on the time-dependent density functional theory is studied in the wavelets formalism used in the BigDFT code, that allows the representations of electronic wave-functions on a simulation grid in real space. The goal of this study is to determine a reference excitation spectrum for a given system and exchange-correlation potential.It appears that only one part of the spectrum can be easily brought to convergence with respect to the input parameters of BigDFT, which are the simulation grid extension and the number of unoccupied continuum orbitals considered in the spectrum calculation. The energy of the last unoccupied orbital used actually proves to be more important as a parameter than this number of unoccupied orbitals. This is justified by the study of the completeness of the basis sets made of the ground state orbitals of the system. This gives another point of view regarding spectrum obtained by using the Gausian basis sets formalism, as the one implemented in the code NWChem.As to the convergence of the spectrum at higher energy, concerning transitions between occupied orbitals and unoccupied orbitals of the continuum, the hope for a convergence faces the problem of the continuum collapse. One therefore has to think of another way of retrieving the data contained in this continuum.The resonant states formalism, whose foundations were laid in the first half of the 20th century, is very encouraging in this regard. A preliminary study in the case of the one-dimension square well potential is therefore presented. The first step consisted in the determination of these resonant states, whose energies and wavefunctions are complex valued in general. Their normalization was also clearly defined. It is then shown, under certain conditions, that the basis set formed by the eigenstates of this potential, including the continuum states, can be efficiently replaced by a discrete and complete basis set made of resonant states. Numerical applications also show that these states can also be advantageously used to define the Green's function or even compute the time propagation of a wavepacket
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Hafver, Andreas. „The formalism of non-commutative quantum mechanics and its extension to many-particle systems“. Thesis, Stellenbosch : University of Stellenbosch, 2010. http://hdl.handle.net/10019.1/5255.
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Thesis (MSc (Physics))--University of Stellenbosch, 2010.ENGLISH ABSTRACT: Non-commutative quantum mechanics is a generalisation of quantum mechanics which incorporates the notion of a fundamental shortest length scale by introducing non-commuting position coordinates. Various theories of quantum gravity indicate the existence of such a shortest length scale in nature. It has furthermore been realised that certain condensed matter systems allow effective descriptions in terms of non-commuting coordinates. As a result, non-commutative quantum mechanics has received increasing attention recently. A consistent formulation and interpretation of non-commutative quantum mechanics, which unambiguously defines position measurement within the existing framework of quantum mechanics, was recently presented by Scholtz et al. This thesis builds on the latter formalism, extends it to many-particle systems and links it up with non-commutative quantum field theory via second quantisation. It is shown that interactions of particles, among themselves and with external potentials, are altered as a result of the fuzziness induced by non-commutativity. For potential scattering, generic increases are found for the differential and total scattering cross sections. Furthermore, the recovery of a scattering potential from scattering data is shown to involve a suppression of high energy contributions, disallowing divergent interaction forces. Likewise, the effective statistical interaction among fermions and bosons is modified, leading to an apparent violation of Pauli’s exclusion principle and foretelling implications for thermodynamics at high densities.
AFRIKAANSE OPSOMMING: Nie-kommutatiewe kwantummeganika is ’n veralgemening van kwantummeganika wat die idee van ’n fundamentele kortste lengteskaal invoer d.m.v. nie-kommuterende ko¨ordinate. Verskeie teorie¨e van kwantum-grawitasie dui op die bestaan van so ’n kortste lengteskaal in die natuur. Dit is verder uitgewys dat sekere gekondenseerde materie sisteme effektiewe beskrywings in terme van nie-kommuterende koordinate toelaat. Gevolglik het die veld van nie-kommutatiewe kwantummeganika onlangs toenemende aandag geniet. ’n Konsistente formulering en interpretasie van nie-kommutatiewe kwantummeganika, wat posisiemetings eenduidig binne bestaande kwantummeganika raamwerke defineer, is onlangs voorgestel deur Scholtz et al. Hierdie tesis brei uit op hierdie formalisme, veralgemeen dit tot veeldeeltjiesisteme en koppel dit aan nie-kommutatiewe kwantumveldeteorie d.m.v. tweede kwantisering. Daar word gewys dat interaksies tussen deeltjies en met eksterne potensiale verander word as gevolg van nie-kommutatiwiteit. Vir potensiale verstrooi ¨ıng verskyn generiese toenames vir die differensi¨ele and totale verstroi¨ıngskanvlak. Verder word gewys dat die herkonstruksie van ’n verstrooi¨ıngspotensiaal vanaf verstrooi¨ıngsdata ’n onderdrukking van ho¨e-energiebydrae behels, wat divergente interaksiekragte verbied. Soortgelyk word die effektiewe statistiese interaksie tussen fermione en bosone verander, wat ly tot ’n skynbare verbreking van Pauli se uitsluitingsbeginsel en dui op verdere gevolge vir termodinamika by ho¨e digthede.
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Lasseri, Raphaël-David. „Distribution spatiale de fermions fortement corrélés en interaction forte : formalisme, méthodes et phénoménologie en structure nucléaire“. Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLS248/document.
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Le noyau est par essence un système complexe, composé de fermions composites fortement corrélés, soumis à la fois aux interactions forte, faible et électromagnétique. La description de sa structure interne est un enjeu important de la physique moderne. Ainsi la manière qu'ont les nucléons de s'organiser au sein des noyaux atomiques est le reflet des corrélations auxquelles ils sont soumis. On comprend alors que la complexité des interactions inter-nucléoniques se traduit par une grande richesse de schémas selon lesquels les nucléons se distribuent dans les systèmes nucléaires. Le noyau révèle une structure délocalisée où les nucléons se répartissent de façon quasi-homogène dans le volume nucléaire. Mais il peut également présenter des sous-structures localisées, appelées clusters ou agrégats nucléaires. Ces travaux s’inscrivent dans le cadre des approches de type champ-moyen relativiste (RMF), permettant un traitement universel de la phénoménologie nucléaire. Dans un premier temps, nous exposerons les éléments de formalisme permettant la construction d’une telle approche en partant des interactions fondamentales qui sous-tendent la dynamique nucléonique au sein des noyaux. Néanmoins ce formalisme ne permet pas de rendre compte des propriétés expérimentales des observables nucléaires : une stricte approche de type champ-moyen, néglige de trop nombreuses classes de corrélations. Nous discuterons alors des méthodes existantes pour prendre en compte ces corrélations, de type particule-trou (déformation) ainsi que de type particules-particules (appariement). Dans un premier temps, une nouvelle méthode diagrammatique, permettant une approche perturbative des corrélations est proposée ainsi qu’une implémentation automatisée associée basée sur une théorie combinatoire. Ensuite, nous reviendrons à un traitement phénoménologique des corrélations particules-trous, pour nous focaliser sur l’impact des corrélations particules-particules. En premier lieu nous discuterons le phénomène de formation de paires nucléoniques en utilisant le langage de la théorie des graphes, langage permettant plusieurs simplifications formelles ainsi qu’une compréhension différentes de l’appariement. Les corrélations d’appariement seront tout d’abord prise en compte par une approche de type Hartree-Bogolioubov relativiste. Toutefois ce formalisme ne conservant pas le nombre de particules, nous présenterons une approche projective permettant de le restaurer. L’effet de cette restauration sur le système sera également étudié. Seront ensuite présentés les différentes implémentations et optimisations numériques, développées pendant cette thèse, pour un traitement général des déformations nucléaires. Munis de ces outils, nous reviendrons sur la formation d’agrégats nucléaires, les clusters, comme phénomène émergent issu de la prise en compte de certaines classes de corrélations. Tout d’abord des mesures de localisations et paramètres quantifiant la dispersion des fonctions d’ondes nucléoniques sont proposées, permettant d’analyser le noyau pour localiser et comprendre l’origine de l’agrégation. L’analyse de ces quantités est présentée et permet la première description unifiée de la formation de clusters aussi bien dans les noyaux légers (Néon, Magnésium) que dans les noyaux lourds émetteurs alpha (Polonium). L’émergence des clusters est ensuite décrite au travers du prisme des transitions de phases quantiques. Un paramètre d’ordre est exhibé ainsi que la caractérisation de ce phénomène en tant que transition de Mott. L’influence des corrélations d’appariement sur la formation de clusters est analysée et une étude précise des propriétés spatiales des paires de nucléons est menée pour plusieurs noyaux dans différentes régions de masses. Enfin une méthode de prise en compte de corrélations à 4-corps, dite de quartet est proposée pour tenter d’expliquer l’émergence des clusters en tant que préformation de particules alphaThe atomic nucleus is intrinsically a complex system, composed of strongly correlated non-elementary fermions, sensitive to strong and electroweak interaction. The description of its internal structure is a major challenge of modern physics. In fact the complexity of the nucleon-nucleon interaction generates correlations which are responsible of the diversity of shapes that the nuclei can adopt. Indeed the nuclei can adopt either quasi-homogeneous shapes when nucleons are delocalized or shapes where spatially localized structure can emerge, namely nuclear clusters. This work is an extension of relativistic mean-fields approach (RMF), which allows an universal treatment of nuclear phenomenology. In a first time we will present the necessary formalism to construct such an approach starting with the fundamental interactions underlying nucleons dynamics within the nucleus. However this approach doesn't allow an accurate reproduction of experimental properties: a purely mean-field approach neglects to many correlations. Existing methods to treat both particle-hole (deformation), particle-particle (pairing) correlations will be discussed. First we will propose a new diagrammatic method, which take correlation into account in a perturbative way, the implementation of this approach using combinatory theory will be discussed. Then we will get back to a phenomenological treatment of particle-hole correlations, to focus on the impact of particle-particle. Formation of nucleonic pair will be discussed in the language of graph theory, allowing several formal simplifications and shed a different light on pairing. Pairing correlations will be at first treated using a relativistic Hartree-Bogolioubov approach. Nevertheless this formalism doesn't conserve particle number, and thus we will present a projective approach to restore it. The effect of this restoration will also be studied. Then to describe general nuclear deformation, several implementations and optimizations developed during this PhD will be presented. With this tools, clusterisation will be investigated as phenomenon emerging for certain class of correlations. Localization measure will be derived allowing a clearer understanding of cluster physics. The analysis of theses quantities makes possible a first unified description of cluster formation both for light nuclei (Neon) or for heavy alpha emitters (Polonium). Cluster emergence will be described as a quantum phase transition, an order parameter will be displayed and this formation will be characterized as a Mott transition. The influence of pairing correlations on cluster formation is studied and a detailed study of pairs spatial properties is performed for nuclei from several mass regions. Lastly a method allowing treatment of 4-body correlations (quartteting) is proposed to explain cluster emergence as alpha particle preformation
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Faber, Carina. „Electrons, excitons et polarons dans les systèmes organiques : approches ab initio à N-corps de type GW et Bethe-Salpeter pour le photovoltaïque organique“. Thesis, Grenoble, 2014. http://www.theses.fr/2014GRENY047/document.
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Cette thèse se propose d'explorer les mérites d'une famille d'approches de simulation quantique ab initio, les théories de perturbation à N-corps, pour l'exploration des propriétés électroniques et optiques de systèmes organiques. Nous avons étudié en particulier l'approximation dite de GW et l'équation de Bethe-Salpeter, très largement utilisées dès les années soixante pour les semiconducteurs de volume, mais dont l'utilisation pour les systèmes organiques moléculaires est très limitée. L'étude de quelques cas d'intérêt pour le photovoltaïque organique, et en particulier de petites molécules pour lesquelles sont disponibles des données expérimentales ou des résultats issus d'approches de chimie quantique, nous ont permis de valider ces approches issues de la physique du solide.Ce doctorat s'inscrit dans le cadre du développement d'un outil de simulation quantique spécifique (le projet FIESTA) dont l'objectif est de combiner les formalismes GW et Bethe-Salpeter avec les techniques de la chimie quantique, c'est-à-dire en particulier l'utilisation de bases localisées analytiques (bases gaussiennes) et des approches de type «résolution de l'identité» pour le traitement des intégrales Coulombiennes. Ce code est aujourd'hui massivement parallélisé, permettant, au delà des études de validation présentées dans ce travail de thèse, l'étude de systèmes complexes comprenant plusieurs centaines d'atomes. En cours de développement, l'incorporation d'approches hybrides combinant mécanique quantique et écrantage à longue portée par des approches modèles de milieu polarisable m'a permis d'une part de me familiariser avec le code et le développement méthodologique, et permet d'autre part d'envisager l'étude de systèmes réalistes en couplage avec leur environnement.Le manuscrit s‘ouvre sur une introduction au photovoltaïque organique afin de mettre en lumière les questionnements spécifiques qui requièrent le développement de nouveaux outils théoriques à la fois fiables en terme de précision et suffisamment efficaces pour traiter des systèmes de grande taille. Le premier chapitre est d'ordre méthodologique et rappelle les fondements des techniques ab initio de type champ-moyen (Hartree, Hartree-Fock et théorie de la fonctionnelle de la densité). En partant des principes de la photoémission, les théories de perturbation à N-corps et la notion de quasi-particule sont ensuite introduites, conduisant aux équations de Hedin et aux approximations GW et COHSEX. De même, à partir de la compréhension d'une expérience d'optique, le traitement des interactions électron-trou est présenté, menant à l'équation de Bethe-Salpeter. Le chapitre 2 introduit brièvement les spécificités techniques liées à l'implémentation des formalismes GW et Bethe-Salpeter. Les propriétés analytiques des bases gaussiennes et les principes mathématiques derrière les techniques de type «résolution de l'identité» et «déformation de contour», sont brièvement décrites. Le troisième chapitre présente les résultats scientifiques obtenus durant cette thèse. Le cas paradigmatique d'un polypeptide model nous permettra de discuter des spécificités de l'approche GW appliquée à des systèmes moléculaires afin d'obtenir des énergies de quasiparticule de bonne qualité. De même, l'utilisation de l'équation de Bethe-Salpeter pour l'obtention du spectre optique de ce système sera présentée, ainsi que le cas d'une famille de colorants d'importance pour les cellules de Graetzel (les coumarines). Finalement, nous explorons dans le cas du fullerène C60 et du graphène le calcul des termes de couplage électron-phonon dans le cadre de l'approche GW, c'est-à-dire au delà des approches standards de type théorie de la fonctionnelle de la densité. Notre étude vise à vérifier si une approximation statique et à écrantage constant au premier ordre permet de garder la qualité des résultats GW pour un coût numérique réduit. Après la conclusion, les appendices donnent le détail de certaines dérivationsThe present thesis aims at exploring the properties and merits of the ab initio Green's function many-body perturbation theory (MBPT) GW and Bethe-Salpeter formalisms, in order to provide a well-grounded and accurate description of the electronic and optical properties of condensed matter systems. While these approaches have been developed for extended inorganic semiconductors and extensively tested on this class of systems since the 60 s, the present work wants to assess their quality for gas phase organic molecules, where systematic studies still remain scarce. By means of small isolated study case molecules, we want to progress in the development of a theoretical framework, allowing an accurate description of complex organic systems of interest for organic photovoltaic devices. This represents the main motivation of this scientific project and we profit here from the wealth of experimental or high-level quantum chemistry reference data, which is available for these small, but paradigmatic study cases.This doctoral thesis came along with the development of a specific tool, the FIESTA package, which is a Gaussian basis implementation of the GW and Bethe-Salpeter formalisms applying resolution of the identity techniques with auxiliary bases and a contour deformation approach to dynamical correlations. Initially conceived as a serial GW code, with limited basis sets and functionalities, the code is now massively parallel and includes the Bethe-Salpeter formalism. The capacity to perform calculations on several hundreds of atoms to moderate costs clearly paves the way to enlarge our studies from simple model molecules to more realistic organic systems. An ongoing project related to the development of discrete polarizable models accounting for the molecular environment allowed me further to become more familiar with the actual implementation and code structure.The manuscript at hand is organized as follows. In an introductory chapter, we briefly present the basic mechanisms characterizing organic solar cells, accentuating the properties which seek for an accurate theoretical description in order to provide some insight into the factors determining solar cell efficiencies. The first chapter of the main part is methodological, including a discussion of the principle features and approximations behind standard mean-field techniques (Hartree, Hartree-Fock, density functional theory). Starting from a description of photoemission experiments, the MBPT and quasiparticle ideas are introduced, leading to the so-called Hedin's equations, the GW method and the COHSEX approach. In order to properly describe optical experiments, electron-hole interactions are included on top of the description of inter-electronic correlations. In this context, the Bethe-Salpeter formalism is introduced, along with an excursus on time-dependent density functional theory. Chapter 2 briefly presents the technical specifications of the GW and Bethe-Salpeter implementation in the FIESTA package. The properties of Gaussian basis sets, the ideas behind the resolution of the identity techniques and finally the contour deformation approach to dynamical correlations are discussed. The third chapter deals with the results obtained during this doctoral thesis. On the electronic structure level, a recent study on a paradigmatic dipeptide molecule will be presented. Further, also its optical properties will be explored, together with an in-depth discussion of charge-transfer excitations in a family of coumarin molecules. Finally, by means of the Buckminster fullerene C60 and the two-dimensional semi-metal graphene, we will analyze the reliability of two many-body formalisms, the so-called static COHSEX and constant-screening approximation, for an efficient calculation of electron-phonon interactions in organic systems at the MBPT level. After a short conclusion, the Appendix containing details and derivations of the formalisms presented before closes this work
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Verrière, Marc. „Description de la dynamique de la fission dans le formalisme de la méthode de la coordonnée génératrice dépendante du temps“. Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLS113/document.
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La fission induite par neutron, découverte il y a plus de 70 ans, a de nombreuses applications, par exemple industrielles pour la production d'énergie, et intervient dans la nucléosynthèse. Cependant, sa description microscopique reste un problème ouvert. En effet, les degrés de liberté qui interviennent dans ce processus dynamique sont complexes. De plus, les noyaux fissiles ont un nombre élevé de nucléons en interaction (>200). Il s'agit donc d'un problème à N-corps quantique. Or, une résolution directe de ce dernier n'est pas possible à l'heure actuelle. Dans ce contexte, la description microscopique de la fission considérée ici est la suivante : la première étape consiste à déterminer un ensemble de configurations de champ moyen qui représentent différentes déformations du noyau, incluant ainsi explicitement les degrés de liberté collectifs qui leur sont associés. Dans la seconde étape, la dynamique est décrite dans cet espace de configurations en utilisant la méthode de la coordonnée génératrice dépendante du temps (TDGCM). L'approximation des recouvrements gaussiens (GOA) est alors utilisée. Cependant, elle introduit une erreur de modèle et limite les extensions comme par exemple la prise en compte explicite de degrés de liberté intrinsèques. Ce travail de thèse a pour objectif de décrire le processus de fission avec la TDGCM sans recourir à la GOA. Cela implique de résoudre l'équation de la dynamique en TDGCM appelée équation de Hill-Wheeler dépendante du temps (TD-HW). Les méthodes d'évaluations des matrices des recouvrements et du hamiltonien collectif sont présentées dans le cas d'une interaction de Gogny. La matrice des recouvrements représente la métrique de l'espace des configurations, et la matrice du hamiltonien collectif contient les couplages énergétiques entre les configurations. Les configurations sont exprimées dans des bases de particules deux à deux distinctes, introduisant des instabilités numériques dans les méthodes d'évaluation standard. Un formalisme adapté à ces bases est proposé permettant d'éliminer ces instabilités. Deux méthodes de résolution de TD-HW sont présentées. La première consiste à calculer l'opérateur d'évolution associé à l'équation de Hill-Wheeler dépendante du temps. Elle est adaptée à un faible nombre de configurations. La seconde utilise un schéma de discrétisation en temps permettant l'inclusion d'un plus grand nombre de configurations dans le modèle. Ce formalisme est ensuite appliqué à la description de la réaction de fission induite par neutron sur le plutonium 239, et une comparaison avec la TDGCM+GOA est effectuéeNuclear fission, where an atomic nucleus separates into two fragments while emitting a large amount of energy, is at the core of many applications in society (energy production) and national security (deterrence, non-proliferation). It is also a key ingredient of the mechanisms of formation of elements in the universe. Yet, nearly 80 years after its experimental discovery its theoretical description in terms of the basic constituents of the nucleus (protons and neutrons) and their interaction remains a challenge. In this thesis, we describe the fission process as follows. In a first step, we use large supercomputers to compute the deformation properties of the nucleus based on our knowledge of nuclear forces. In a second step, we simulate the time evolution of the system from its ground state up to the fragments separation with a fully quantum-mechanical approach called the time-dependent generator coordinate method (TDGCM). While results are in good qualitative agreement with experimental data, the implementation of the TDGCM so far had been greatly simplified using what is known as the Gaussian overlap approximation (GOA). We also developed the formalism and a numerical implementation of the exact TDGCM - without the GOA. This will allow the first systematic validation of that approximation and an assessment of the resulting theoretical uncertainties. The second chapter presents the description of the neutron induced fission process using the TDGCM+GOA. The third one introduces the developments carried out in this thesis allowing the description of the fission process with the TDGCM without the GOA. The last chapter shows the first results obtained with this approach
Bücher zum Thema "Many-Body formalisms"
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Boudreau, Joseph F., und Eric S. Swanson. Quantum mechanics II–many body systems. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198708636.003.0023.
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Chapter 23 develops formalism relevant to atomic and molecular electronic structure. A review of the product Ansatz, the Slater determinant, and atomic configurations is followed by applications to small atoms. Then the self-consistent Hartree-Fock method is introduced and applied to larger atoms. Molecular structure is addressed by introducing an adiabatic separation of scales and the construction of molecular orbitals. The use of specialized bases for molecular computations is also discussed. Density functional theory and its application to complicated molecules is introduced and the local density approximation and the Kohn-Sham procedure for solving the functional equations are explained. Techniques for moving beyond the local density approximation are briefly reviewed.
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Morawetz, Klaus. Variational Techniques of Many-Body Theory. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198797241.003.0011.
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The variational technique for nonequilibrium Green’s functions is derived resulting in the Hedin equations. This allows exploring of the high-density limit of diagrammatic expansions. Nonequilibrium Ward identities are presented. An asymmetric cummulant expansion of many-body Greens functions is developed resulting in asymmetric internal propagators which will become important for a consistent theory of pairing and condensation. All known approximations for the selfenergy are derived and reviewed with respect to asymmetric corrected propagators. The linear response formalism is discussed and the response for finite systems is presented. The link to functional renormalisation techniques is provided and integration of high-energy modes is discussed with hard and soft cut-off procedures.
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Succi, Sauro. QLB for Quantum Many-Body and Quantum Field Theory. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780199592357.003.0033.
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Chapter 32 expounded the basic theory of quantum LB for the case of relativistic and non-relativistic wavefunctions, namely single-particle quantum mechanics. This chapter goes on to cover extensions of the quantum LB formalism to the overly challenging arena of quantum many-body problems and quantum field theory, along with an appraisal of prospective quantum computing implementations. Solving the single particle Schrodinger, or Dirac, equation in three dimensions is a computationally demanding task. This task, however, pales in front of the ordeal of solving the Schrodinger equation for the quantum many-body problem, namely a collection of many quantum particles, typically nuclei and electrons in a given atom or molecule.
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Thygesen, K. S., und A. Rubio. Correlated electron transport in molecular junctions. Herausgegeben von A. V. Narlikar und Y. Y. Fu. Oxford University Press, 2017. http://dx.doi.org/10.1093/oxfordhb/9780199533046.013.23.
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This article focuses on correlated electron transport in molecular junctions. More specifically, it considers how electronic correlation effects can be included in transport calculations using many-body perturbation theory within the Keldysh non-equilibrium Green’s function formalism. The article uses the GW self-energy method (G denotes the Green’s function and W is the screened interaction) which has been successfully applied to describe quasi-particle excitations in periodic solids. It begins by formulating the quantum-transport problem and introducing the non-equilibrium Green’s function formalism. It then derives an expression for the current within the NEGF formalism that holds for interactions in the central region. It also combines the GW scheme with a Wannier function basis set to study electron transport through two prototypical junctions: a benzene molecule coupled to featureless leads and a hydrogen molecule between two semi-infinite platinum chains. The results are analyzed using a generic two-level model of a molecular junction.
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Morawetz, Klaus. Interacting Systems far from Equilibrium. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198797241.001.0001.
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In quantum statistics based on many-body Green’s functions, the effective medium is represented by the selfenergy. This book aims to discuss the selfenergy from this point of view. The knowledge of the exact selfenergy is equivalent to the knowledge of the exact correlation function from which one can evaluate any single-particle observable. Complete interpretations of the selfenergy are as rich as the properties of the many-body systems. It will be shown that classical features are helpful to understand the selfenergy, but in many cases we have to include additional aspects describing the internal dynamics of the interaction. The inductive presentation introduces the concept of Ludwig Boltzmann to describe correlations by the scattering of many particles from elementary principles up to refined approximations of many-body quantum systems. The ultimate goal is to contribute to the understanding of the time-dependent formation of correlations. Within this book an up-to-date most simple formalism of nonequilibrium Green’s functions is presented to cover different applications ranging from solid state physics (impurity scattering, semiconductor, superconductivity, Bose–Einstein condensation, spin-orbit coupled systems), plasma physics (screening, transport in magnetic fields), cold atoms in optical lattices up to nuclear reactions (heavy-ion collisions). Both possibilities are provided, to learn the quantum kinetic theory in terms of Green’s functions from the basics using experiences with phenomena, and experienced researchers can find a framework to develop and to apply the quantum many-body theory straight to versatile phenomena.
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Eriksson, Olle, Anders Bergman, Lars Bergqvist und Johan Hellsvik. Density Functional Theory. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780198788669.003.0001.
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Density functional theory (DFT) has established itself as a very capable platform for modelling from first principles electronic, optical, mechanical and structural properties of materials. Starting out from the Dirac equation for the many-body system of electrons and nuclei, an effective theory has been developed allowing for materials specific and parameter free simulations of non-magnetic and magnetic solid matter. In this Chapter an introduction will be given to DFT, the Hohenberg-Kohn theorems, the Kohn-Sham equation, and the formalism for how to deal with non-collinear magnetism.
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Morawetz, Klaus. Scattering on a Single Impurity. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198797241.003.0004.
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Evolution of a many-body system consists of permanent collisions among particles. Looking at the motion of a single particle, one can identify encounters by which a particle abruptly changes the direction of flight, these are seen as true collisions, and small-angle encounters, which in sum act as an applied force rather than randomising collisions. The scattering on impurities is used to introduce the mentioned mechanisms and, in particular, to show how they affect each other. Point impurities are assumed, i.e. impurities the potential of which is restricted to a single atomic site of the crystal lattice. In this case interaction potentials never overlap and many-body effects are due to nonlocal character of the quantum particle. To introduce elementary components of the formalism, in this chapter we first describe the interaction of an electron with a single impurity. Lippman–Schwinger equations are derived and the physics behind the collision delay, dissipativeness and optical theorems is explored.
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Succi, Sauro. LBE for Generalized Hydrodynamics. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780199592357.003.0025.
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This chapter presents the main techniques to incorporate the effects of external and/or internal forces within the LB formalism. This is a very important task, for it permits us to access a wide body of generalized hydrodynamic applications whereby fluid motion couples to a variety of additional physical aspects, such as gravitational and electric fields, potential energy interactions, chemical reactions and many others. It should be emphasized that while hosting a broader and richer phenomenology than “plain” hydrodynamics, generalized hydrodynamics still fits the hydrodynamic picture of weak departure from suitably generalized local equilibria. This class is all but an academic curiosity; for instance, it is central to the fast-growing science of Soft Matter, a scientific discipline which has received an impressive boost in the past decades, under the drive of micro- and nanotechnological developments and major strides in biology and life sciences at large.
Buchteile zum Thema "Many-Body formalisms"
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Hecht, K. T. „Many-Body Formalism“. In Quantum Mechanics, 721–38. New York, NY: Springer New York, 2000. http://dx.doi.org/10.1007/978-1-4612-1272-0_78.
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Lindgren, Ingvar. „Time-Independent Formalism“. In Relativistic Many-Body Theory, 11–41. Cham: Springer International Publishing, 2016. http://dx.doi.org/10.1007/978-3-319-15386-5_2.
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Lindgren, Ingvar. „Time-Dependent Formalism“. In Relativistic Many-Body Theory, 43–53. Cham: Springer International Publishing, 2016. http://dx.doi.org/10.1007/978-3-319-15386-5_3.
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Lindgren, Ingvar. „Time-Independent Formalism“. In Relativistic Many-Body Theory, 13–46. New York, NY: Springer New York, 2011. http://dx.doi.org/10.1007/978-1-4419-8309-1_2.
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Lindgren, Ingvar. „Time-Dependent Formalism“. In Relativistic Many-Body Theory, 47–56. New York, NY: Springer New York, 2011. http://dx.doi.org/10.1007/978-1-4419-8309-1_3.
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Lindgren, Ingvar, und John Morrison. „Second Quantization and the Particle-Hole Formalism“. In Atomic Many-Body Theory, 224–50. Berlin, Heidelberg: Springer Berlin Heidelberg, 1986. http://dx.doi.org/10.1007/978-3-642-61640-2_11.
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Iafrate, G. J., J. B. Krieger und Y. Li. „Many-Body Effects and Density Functional Formalism in Nanoelectronics“. In Computational Electronics, 183–88. Boston, MA: Springer US, 1991. http://dx.doi.org/10.1007/978-1-4757-2124-9_37.
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Randazzo, Juan M., Carlos Marante, Siddhartha Chattopadhyay, Heman Gharibnejad, Barry I. Schneider, Jeppe Olsen und Luca Argenti. „ASTRA, A Transition Density Matrix Approach to the Interaction of Attosecond Radiation with Atoms and Molecules“. In Springer Proceedings in Physics, 115–27. Cham: Springer International Publishing, 2023. http://dx.doi.org/10.1007/978-3-031-47938-0_11.
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AbstractA new formalism and computer code, ASTRA (AttoSecond TRAnsitions), has been developed to treat the interactions of short, intense radiation with molecules. The formalism makes extensive use of transition density matrices, computed using a state-of-the-art quantum chemistry code (LUCIA), to efficiently calculate the many-body inter-channel-coupling interactions required to simulate the highly correlated electron dynamics due to atoms and molecules exposed to attosecond laser radiation.
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Piecuch, P. „Cartesian-Spherical Transformation Formalism and the Theoretical Insight into Many-Body Long-Range Forces of the Electrostatic Origin in Multimolecular Systems“. In Interactions of Water in Ionic and Nonionic Hydrates, 299–302. Berlin, Heidelberg: Springer Berlin Heidelberg, 1987. http://dx.doi.org/10.1007/978-3-642-72701-6_57.
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Zinn-Justin, Jean. „Quantum statistical physics: Functional integration formalism“. In Quantum Field Theory and Critical Phenomena, 64–89. Oxford University Press, 2021. http://dx.doi.org/10.1093/oso/9780198834625.003.0004.
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The functional integral representation of the density matrix at thermal equilibrium in non-relativistic quantum mechanics (QM) with many degrees of freedom, in the grand canonical formulation is introduced. In QM, Hamiltonians H(p,q) can be also expressed in terms of creation and annihilation operators, a method adapted to the study of perturbed harmonic oscillators. In the holomorphic formalism, quantum operators act by multiplication and differentiation on a vector space of analytic functions. Alternatively, they can also be represented by kernels, functions of complex variables that correspond in the classical limit to a complex parametrization of phase space. The formalism is adapted to the description of many-body boson systems. To this formalism corresponds a path integral representation of the density matrix at thermal equilibrium, where paths belong to complex spaces, instead of the more usual position–momentum phase space. A parallel formalism can be set up to describe systems with many fermion degrees of freedom, with Grassmann variables replacing complex variables. Both formalisms can be generalized to quantum gases of Bose and Fermi particles in the grand canonical formulation. Field integral representations of the corresponding quantum partition functions are derived.
Konferenzberichte zum Thema "Many-Body formalisms"
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IMAMOVIC–TOMASOVIC, M., und A. GRIFFIN. „GENERALIZED BOLTZMANN EQUATION FOR A TRAPPED BOSE–CONDENSED GAS USING THE KADANOFF–BAYM FORMALISM“. In Proceedings of the Conference “Kadanoff-Baym Equations: Progress and Perspectives for Many-Body Physics”. WORLD SCIENTIFIC, 2000. http://dx.doi.org/10.1142/9789812793812_0032.
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Koch, Stephan W., Hartmut Haug und Murray Sargent. „Semiconductor laser theory with many-body effects“. In OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1988. http://dx.doi.org/10.1364/oam.1988.mj5.
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A theory of a semiconductor laser is developed that includes the many-body effects due to Coulomb interactions. The theory is valid for both 3-D bulk semiconductors as well as quasi-2-D quantum well structures. We emphasize plasma density-dependent band gap renormalization, broadening due to intraband scattering, and electron–hole Coulomb enhancement. The very short intraband scattering relaxation time allows us to eliminate the interband polarization adiabatically and to introduce a hydrodynamic description of the intraband kinetics. From this general formulation a diffusion equation for the carrier density is derived. The resulting diffusion coefficient decreases with carrier density and laser intensity due to the reduction of the electron drift. We use our theory in the problem of laser gain, index, and side mode instabilities. We show that near the laser operating point, our many-body theory can be approximated by a simple rate equation formalism. However, in contrast to the usual rate-equation theory, the semiconductor rate constants are functions of temperature, tuning, and carrier density.
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Khude, Naresh, Dan Melanz, Ilinca Stanciulescu und Dan Negrut. „A Parallel GPU Implementation of the Absolute Nodal Coordinate Formulation With a Frictional/Contact Model for the Simulation of Large Flexible Body Systems“. In ASME 2011 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference. ASMEDC, 2011. http://dx.doi.org/10.1115/detc2011-48816.
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This contribution discusses how a flexible body formalism, specifically, the Absolute Nodal Coordinate Formulation (ANCF), is combined with a frictional/contact model using the Discrete Element Method (DEM) to address many-body dynamics problems; i.e., problems with hundreds of thousands of rigid and deformable bodies. Since the computational effort associated with these problems is significant, the analytical framework is implemented to leverage the computational power available on today’s commodity Graphical Processing Unit (GPU) cards. The code developed is validated against ANSYS and FEAP results. The resulting simulation capability is demonstrated in conjunction with hair simulation.
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Bozzato, Loris, Thomas Eiter und Luciano Serafini. „Enhancing Context Knowledge Repositories with Justifiable Exceptions (Extended Abstract)“. In Twenty-Seventh International Joint Conference on Artificial Intelligence {IJCAI-18}. California: International Joint Conferences on Artificial Intelligence Organization, 2018. http://dx.doi.org/10.24963/ijcai.2018/786.
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The Contextualized Knowledge Repository (CKR) framework was conceived as a logic-based approach for representing context dependent knowledge, which is a well-known area of study in AI. The framework has a two-layer structure with a global context that contains context-independent knowledge and meta-information about the contexts, and a set of local contexts with specific knowledge bases. In many practical cases, it is desirable that inherited global knowledge can be "overridden" at the local level. In order to address this need, we present an extension of CKR with global defeasible axioms: these axioms locally apply to (tuples of) individuals unless an exception for overriding exists; such an exception, however, requires a justification that is provable from the knowledge base. We formalize this intuition and study its semantic and computational properties. Furthermore, we present a translation of extended CKRs to datalog programs under the answer set (i.e., stable) semantics and we present an implementation prototype. Our work adds to the body of results on using deductive database technology in these areas, and provides an expressive formalism for exception handling by overriding.