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Although selected configuration interaction (SCI) algorithms can tackle much larger Hilbert spaces than the conventional full CI (FCI) method, the scaling of their computational cost with respect to the system size remains inherently exponential. Additionally, inaccuracies in describing the correlation hole at small interelectronic distances lead to the slow convergence of the electronic energy relative to the size of the one-electron basis set. To alleviate these effects, we show that the non-Hermitian, transcorrelated (TC) version of SCI significantly compactifies the determinant space, allowing to reach a given accuracy with a much smaller number of determinants. Furthermore, we note a significant acceleration in the convergence of the TC-SCI energy as the basis set size increases. The extent of this compression and the energy convergence rate are closely linked to the accuracy of the correlation factor used for the similarity transformation of the Coulombic Hamiltonian. Our systematic investigation of small molecular systems in increasingly large basis sets illustrates the magnitude of these effects.
In this article, we explore the construction of Hamiltonians with long-range interactions and their corrections using the short-range behavior of the wave function. A key aspect of our investigation is the examination of the one-particle potential, kept constant in our previous work, and the effects of its optimization on the adiabatic connection. Our methodology involves the use of a parameter-dependent potential dependent on a single parameter to facilitate practical computations. We analyze the energy errors and densities in a two-electron system (harmonium) under various conditions, employing different confinement potentials and interaction parameters. The study reveals that while the mean-field potential improves the expectation value of the physical Hamiltonian, it does not necessarily improve the energy of the system within the bounds of chemical accuracy. We also delve into the impact of density variations in adiabatic connections, challenging the common assumption that a mean field improves results. Our findings indicate that as long as energy errors remain within chemical accuracy, the mean field does not significantly outperform a bare potential. This observation is attributed to the effectiveness of corrections based on the short-range behavior of the wave function, a universal characteristic that diminishes the distinction between using a mean field or not.
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.
At very low density, the electrons in a uniform electron gas spontaneously break symmetry and form a crystalline lattice called a Wigner crystal. But which type of crystal will the electrons form? We report a numerical study of the density profiles of fragments of Wigner crystals from first principles. To simulate Wigner fragments, we use Clifford periodic boundary conditions and a renormalized distance in the Coulomb potential. Moreover, we show that high-spin restricted open-shell Hartree–Fock theory becomes exact in the low-density limit. We are thus able to accurately capture the localization in two-dimensional Wigner fragments with many electrons. No assumptions about the positions where the electrons will localize are made. The density profiles we obtain emerge naturally when we minimize the total energy of the system. We clearly observe the emergence of the hexagonal crystal structure, which has been predicted to be the ground-state structure of the two-dimensional Wigner crystal.
Leptoquark models may explain deviations from the standard model observed in decay processes involving heavy quarks at high-energy colliders. Such models give rise to low-energy parity- and time-reversal-violating phenomena in atoms and molecules. One of the leading effects among these phenomena is the nucleon-electron tensor-pseudotensor interaction when the low-energy experimental probe uses a quantum state of an atom or molecule predominantly characterized by closed electron shells. In the present paper the molecular interaction constant for the nucleon-electron tensor-pseudotensor interaction in the thallium-fluoride molecule—used as such a sensitive probe by the CeNTREX collaboration [O. Grasdijk et al., Quantum Sci. Technol. 6, 044007 (2021)]—is calculated employing highly correlated relativistic many-body theory. Accounting for up to quintuple excitations in the wave-function expansion the final result is WT(Tl)=−6.25±0.31 (10−13⟨Σ⟩A a.u.) Interelectron correlation effects on the tensor-pseudotensor interaction are studied rigorously in a molecule.
Sujets
États excités
AROMATIC-MOLECULES
Auto-énergie
Dispersion coefficients
Parallel speedup
AB-INITIO CALCULATION
QSAR
Chemical concepts
3115ag
Atrazine-cations complexes
Azide Anion
3115ae
Approximation GW
Atrazine
Atomic data
Quantum chemistry
Diffusion Monte Carlo
Argile
3115bw
Electron correlation
Relativistic quantum chemistry
Time-dependent density-functional theory
Atomic processes
Coupled cluster calculations
Fonction de Green
A priori Localization
Configuration Interaction
Dirac equation
Quantum Monte Carlo
X-ray spectroscopy
Molecular descriptors
Density functional theory
Analytic gradient
Valence bond
Atomic and molecular structure and dynamics
Spin-orbit interactions
Configuration interaction
Chimie quantique
Atomic charges
Basis set requirements
Pesticide
Excited states
Abiotic degradation
Configuration interactions
Atoms
Acrolein
Petascale
Atomic charges chemical concepts maximum probability domain population
Ground states
Xenon
AB-INITIO
3315Fm
Diatomic molecules
3115aj
Line formation
Ion
Atom
Single-core optimization
3115vn
BSM physics
Polarizabilities
Corrélation électronique
Parity violation
Electron electric moment
Atomic and molecular collisions
Perturbation theory
Hyperfine structure
Adiabatic connection
Aimantation
Argon
BENZENE MOLECULE
Range separation
Time reversal violation
BIOMOLECULAR HOMOCHIRALITY
Coupled cluster
Relativistic corrections
A posteriori Localization
Wave functions
Molecular properties
Green's function
Mécanique quantique relativiste
Biodegradation
Anderson mechanism
Relativistic quantum mechanics
Electron electric dipole moment
ALGORITHM
Quantum Chemistry
Ab initio calculation
3115am
3115vj
Dipole
CIPSI
Numerical calculations
Rydberg states
CP violation
Large systems
Pesticides Metabolites Clustering Molecular modeling Environmental fate Partial least squares
3470+e
New physics
Carbon Nanotubes