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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
Nucléaire
Relaxation
Extended time-dependent Hartree-Fock
Molecular dynamics
Oxyde de nickel
Density Functional Theory
Electronic emission
Instabilité
Dissipative effects
Energy spectrum
TDDFT
Méchanismes d'ionisation
Champ-moyen
CAO
Electron emission
Time-dependent density-functional theory
Méthode multiréférence
GW approximation
Multirefence methods
Correction d'auto-interaction
Deposition
Green's function
Interactions de photons avec des systèmes libres
Electronic excitation
Instability
Electron correlation
Fission
Landau damping
Clusters
Optical response
Electronic properties of metal clusters and organic molecules
Aggregates
Au-delà du champ moyen
MBPT
Molecules
Electron-surface collision
Hierarchical method
Photo-electron distributions
Nanoplasma
Deposition dynamics
Dissipation
Semiclassic
Corrélations
Embedded metal cluster
Corrélation forte
Numbers 3360+q
Mean-field
Inverse bremsstrahlung collisions
Fonction de Green
Théorie de la fonctionnelle de la densité
Activation neutronique
Ar environment
Density-functional theory
Photo-Electron Spectrum
FOS Physical sciences
Metal clusters
3115ee
Electronic properties of sodium and carbon clusters
Ionization mechanisms
Neutron Induced Activation
Corrélations dynamiques
Coulomb presssure
Agrégats
Nuclear
Explosion coulombienne
Angle-resolved photoelectron spectroscopy
Greens function methods
Collisional time-dependent Hartree-Fock
Neutronique
Coulomb explosion
Neutronic
Hubbard model
Monte-Carlo
Nickel oxide
Molecular irradiation
Matel clusters
Modèle de Hubbard
Hierarchical model
Photon interactions with free systems
Diffusion
3640Cg
Dynamique moléculaire
Chaos
Metal cluster
Damping
Irradiation moléculaire
Atom laser
High intensity lasers
Méthodes des fonctions de Green
Lasers intenses
Effets dissipatifs
Agregats
Environment
Matrice densité
Dynamics
Laser
Collision frequency
Approximation GW
Electric field
3620Kd