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