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