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