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