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