Loading...
Derniers dépôts, tout type de documents
We systematically study a set of strongly polar heteronuclear diatomic molecules composed of laser-coolable atoms for their suitability as sensitive probes of new charge-parity violation in the hadron sector of matter. Using relativistic general-excitation-rank configuration-interaction theory we single out the molecule francium-silver (FrAg) as the most promising system in this set and calculate its nuclear Schiff-moment interaction constant to WFrAgSM(Fr)=30168±2504a.u. for the target nucleus Fr. Our work includes the development of system-tailored atomic Gaussian basis sets for the target atom in each respective molecule.
We performed several types of ab initio calculations, from Hartree-Fock to Complete-Active-Space second-order perturbation theory and Coupled Cluster, on compact clusters of stoichiometry XY, where X and Y are atoms belonging to the second row of the periodic table. More precisely, we considered the “cubic” structures of three isoelectronic groups, having a total of 48, 52, and 56-electrons, respectively. Notice that the highly symmetric cubic clusters of type X are characterized by an symmetry group, while the XY structures, with XY, have at most a symmetry. Binding energies and wave function analysis of these clusters have been performed, in order to investigate the nature, and the electron delocalization of these systems and establish a comparison between them. To this purpose, we also computed the Total-Position Spread tensor for each structure, a quantity which is related to the multi-reference nature of a system wave function.
Charged and electronically excitations processes are central to chemistry, physics and biology, playing a key role in ubiquitous processes such as photochemistry, catalysis and solar cell technology. However, defining an effective method that reliably provides accurate excited-state and ionization energies remains a major challenge in theoretical chemistry. Originally developed in the framework of nuclear physics and then used in the condensed matter community, the use of Green's function methods in quantum chemistry has significantly developed in recent years. Indeed, Green's function methods have garnered considerable interest due to their ability to target both charged and neutral excitations. The pillar of Green's function methods is the one-body Green's function. It has the ability to provide the charged excitations meaning the addition or the removal of an electron in the molecule of the system in a single calculation as measured in direct or inverse photoemission spectroscopy. This avoids using traditional quantum chemistry methods where one has to perform separate calculations on the neutral and ionized species. The calculation of charged excitations needs to solve the Dyson equation that links the one-body Green's function to the so-called self-energy. The computation of neutral excitations, meaning the promotion of an electron to an excited state of the molecule, needs the use of the two-body Green's function through its connection with the so-called kernel by the Bethe-Salpeter equation. Unfortunately, the exact self-energy and kernel are not known and approximations need to be done. In this thesis we explore performances of different approximations for the self-energy and kernel by comparing with various well known quantum chemistry methods by applying these approximations on various atomic and molecular systems. Moreover, we identify the unphysical discontinuities that we encounter in various physical quantities when using approximations for the self-energy and propose a way to avoid such issues. Then, we investigate the connections between various Green's function approximations. Finally, different methods seen in this thesis are gathered to form an open source quantum chemistry software with a strong emphasis on helping students and newcomers in the field to develop their own ideas.
The cumulant expansion of the Green's function is a computationally efficient beyond-$GW$ approach renowned for its significant enhancement of satellite features in materials. In contrast to the ubiquitous $GW$ approximation of many-body perturbation theory, \textit{ab initio} cumulant expansions performed on top of $GW$ ($GW$+C) have demonstrated the capability to handle multi-particle processes by incorporating higher-order correlation effects or vertex corrections, yielding better agreements between experiment and theory for satellite structures. While widely employed in condensed matter physics, very few applications of $GW$+C have been published on molecular systems. Here, we assess the performance of this scheme on a series of 10-electron molecular systems (\ce{Ne}, \ce{HF}, \ce{H2O}, \ce{NH3}, and \ce{CH4}) where full configuration interaction estimates of the outer-valence quasiparticle and satellite energies are available.
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.
Sujets
Coupled cluster
Basis set requirements
Rydberg states
Molecular descriptors
A posteriori Localization
Wave functions
BENZENE MOLECULE
3115ag
Configuration interaction
États excités
BIOMOLECULAR HOMOCHIRALITY
ALGORITHM
Relativistic corrections
AROMATIC-MOLECULES
Basis sets
Excited states
3470+e
QSAR
Carbon Nanotubes
Chemical concepts
Configuration interactions
Large systems
Xenon
Diffusion Monte Carlo
Diatomic molecules
Mécanique quantique relativiste
Molecular properties
3115vn
Dispersion coefficients
Atomic charges chemical concepts maximum probability domain population
3115ae
Ground states
Parallel speedup
Atomic and molecular collisions
Dirac equation
Green's function
Electron electric dipole moment
Electron correlation
Perturbation theory
Biodegradation
Atomic charges
Argile
Atrazine
Pesticides Metabolites Clustering Molecular modeling Environmental fate Partial least squares
Atom
Chimie quantique
X-ray spectroscopy
Abiotic degradation
Anderson mechanism
Time reversal violation
AB-INITIO
3115aj
Density functional theory
Quantum Chemistry
CP violation
AB-INITIO CALCULATION
New physics
Hyperfine structure
3115am
Quantum Monte Carlo
Quantum chemistry
Auto-énergie
Configuration Interaction
Ab initio calculation
Polarizabilities
Analytic gradient
Atomic processes
Single-core optimization
Electron electric moment
Argon
Benchmarks
Acrolein
3315Fm
Atrazine-cations complexes
CIPSI
A priori Localization
Atoms
Parity violation
Ion
Range separation
Coupled cluster calculations
Corrélation électronique
Petascale
BSM physics
Pesticide
Fonction de Green
Atomic and molecular structure and dynamics
Time-dependent density-functional theory
Valence bond
Atomic data
Relativistic quantum mechanics
Dipole
Azide Anion
Numerical calculations
Relativistic quantum chemistry
3115vj
Aimantation
Spin-orbit interactions
Line formation
3115bw