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