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The subject of the thesis focuses on new approximations studied in a formalism based on a perturbation theory allowing to describe the electronic properties of many-body systems in an approximate way. We excite a system with a small disturbance, by sending light on it or by applying a weak electric field to it, for example and the system "responds" to the disturbance, in the framework of linear response, which means that the response of the system is proportional to the disturbance. The goal is to determine what we call the neutral excitations or bound states of the system, and more particularly the single excitations. These correspond to the transitions from the ground state to an excited state. To do this, we describe in a simplified way the interactions of the particles of a many-body system using an effective interaction that we average over the whole system. The objective of such an approach is to be able to study a system without having to use the exact formalism which consists in diagonalizing the N-body Hamiltonian, which is not possible for systems with more than two particles.
We present the multi-channel Dyson equation that combines two or more many-body Green's functions to describe the electronic structure of materials. In this thesis, we use it to model photoemission spectra by coupling the one-body Green's function with the three-body Green's function and to model neutral excitation by coupling the two-body Green's function with the four-body Green's function . We demonstrate that, unlike methods using only the one-body Green's function, our approach puts the description of quasiparticles and satellites on an equal footing. We propose a multi-channel self-energy that is static and only contains the bare Coulomb interaction, making frequency convolutions and self-consistency unnecessary. Despite its simplicity, we demonstrate with a diagrammatic analysis that the physics it describes is extremely rich. Finally, we present a framework based on an effective Hamiltonian that can be solved for any many-body system using standard numerical tools. We illustrate our approach by applying it to the Hubbard dimer and show that it is exact both at 1/4 and 1/2 filling.
We present the second release of the real-time time-dependent density functional theory code “Quantum Dissipative Dynamics” (QDD). It augments the first version [1] by a parallelization on a GPU coded with CUDA fortran. The extension focuses on the dynamical part only because this is the most time consuming part when applying the QDD code. The performance of the new GPU implementation as compared to OpenMP parallelization has been tested and checked on a couple of small sodium clusters and small covalent molecules. OpenMP parallelization allows a speed-up by one order of magnitude in average, as compared to a sequential computation. The use of a GPU permits a gain of an additional order of magnitude. The performance gain outweighs even the larger energy consumption of a GPU. The impressive speed-up opens the door for more demanding applications, not affordable before
We present the multi-channel Dyson equation that combines two or more many-body Green's functions to describe the electronic structure of materials. In this work we use it to model photoemission spectra by coupling the one-body Green's function with the three-body Green's function. We demonstrate that, unlike methods using only the one-body Green's function, our approach puts the description of quasiparticles and satellites on an equal footing. We propose a multi-channel self-energy that is static and only contains the bare Coulomb interaction, making frequency convolutions and self-consistency unnecessary. Despite its simplicity, we demonstrate with a diagrammatic analysis that the physics it describes is extremely rich. Finally, we present a framework based on an effective Hamiltonian that can be solved for any many-body system using standard numerical tools. We illustrate our approach by applying it to the Hubbard dimer and show that it is exact both at 1/4 and 1/2 filling.
Sujets
Energy spectrum
Optical response
Electron emission
Electron correlation
Molecules
Ar environment
Hierarchical method
Landau damping
Green's function
Fission
Interactions de photons avec des systèmes libres
Metal cluster
Ionization mechanisms
Nucléaire
Collisional time-dependent Hartree-Fock
Nuclear
Molecular irradiation
Density-functional theory
Clusters
Correction d'auto-interaction
Hubbard model
Time-dependent density-functional theory
Collision frequency
Electronic properties of metal clusters and organic molecules
Hierarchical model
Effets dissipatifs
Electric field
Théorie de la fonctionnelle de la densité
Greens function methods
Coulomb presssure
Environment
FOS Physical sciences
Matel clusters
GW approximation
Chaos
High intensity lasers
Lasers intenses
Coulomb explosion
Dynamics
TDDFT
MBPT
Agrégats
Multirefence methods
Dissipative effects
3115ee
Corrélations
Méchanismes d'ionisation
Activation neutronique
Au-delà du champ moyen
Irradiation moléculaire
Méthodes des fonctions de Green
CAO
Diffusion
3620Kd
Neutronic
Neutron Induced Activation
Deposition dynamics
Molecular dynamics
Damping
Oxyde de nickel
Photon interactions with free systems
Numbers 3360+q
Deposition
Angle-resolved photoelectron spectroscopy
Instability
Inverse bremsstrahlung collisions
Matrice densité
Instabilité
Aggregates
Méthode multiréférence
Photo-electron distributions
Relaxation
Semiclassic
Electronic emission
Electronic excitation
Dynamique moléculaire
Metal clusters
Explosion coulombienne
Corrélations dynamiques
Approximation GW
Nickel oxide
Dissipation
Agregats
Photo-Electron Spectrum
Champ-moyen
Density Functional Theory
Mean-field
Corrélation forte
Fonction de Green
Extended time-dependent Hartree-Fock
Nanoplasma
Modèle de Hubbard
Atom laser
Embedded metal cluster
Electronic properties of sodium and carbon clusters
Monte-Carlo
Electron-surface collision
3640Cg
Laser
Neutronique