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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.

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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.

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In the realm of photochemistry, the significance of double excitations (also known as doubly-excited states), where two electrons are concurrently elevated to higher energy levels, lies in their involvement in key electronic transitions essential in light-induced chemical reactions as well as their challenging nature from the computational theoretical chemistry point of view. Based on state-of-the-art electronic structure methods (such as high-order coupled-cluster, selected configuration interaction, and multiconfigurational methods), we improve and expand our prior set of accurate reference excitation energies for electronic states exhibiting a substantial amount of double excitations [http://dx.doi.org/10.1021/acs.jctc.8b01205; Loos et al. J. Chem. Theory Comput. 2019, 15, 1939]. This extended collection encompasses 47 electronic transitions across 26 molecular systems that we separate into two distinct subsets: (i) 28 "genuine" doubly-excited states where the transitions almost exclusively involve doubly-excited configurations and (ii) 19 "partial" doubly-excited states which exhibit a more balanced character between singly- and doubly-excited configurations. For each subset, we assess the performance of high-order coupled-cluster (CC3, CCSDT, CC4, and CCSDTQ) and multiconfigurational methods (CASPT2, CASPT3, PC-NEVPT2, and SC-NEVPT2). Using as a probe the percentage of single excitations involved in a given transition ($\%T_1$) computed at the CC3 level, we also propose a simple correction that reduces the errors of CC3 by a factor of 3, for both sets of excitations. We hope that this more complete and diverse compilation of double excitations will help future developments of electronic excited-state methodologies.

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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.

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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.

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Subjets

Range separation Diatomic molecules Analytic gradient Atomic and molecular collisions Large systems Time-dependent density-functional theory Line formation Excited states États excités Diffusion Monte Carlo Perturbation theory Relativistic corrections Spin-orbit interactions Acrolein Auto-énergie Polarizabilities Hyperfine structure Corrélation électronique Quantum Chemistry Atoms Anderson mechanism Single-core optimization 3115ae Parallel speedup Green's function Configuration interactions Electron electric moment 3115am Basis set requirements Configuration interaction BSM physics Relativistic quantum chemistry Carbon Nanotubes Dirac equation Parity violation Atomic charges Coupled cluster BIOMOLECULAR HOMOCHIRALITY Rydberg states Petascale Atomic processes Molecular descriptors Atrazine-cations complexes Molecular properties Dispersion coefficients Time reversal violation AB-INITIO CALCULATION Quantum Monte Carlo New physics 3115vj Chemical concepts Mécanique quantique relativiste 3115ag A posteriori Localization Ab initio calculation Atomic charges chemical concepts maximum probability domain population 3115bw 3315Fm Aimantation Argile Basis sets Quantum chemistry Azide Anion Relativistic quantum mechanics Fonction de Green Pesticides Metabolites Clustering Molecular modeling Environmental fate Partial least squares Atomic and molecular structure and dynamics Abiotic degradation Atom Ground states Benchmarks Biodegradation CIPSI QSAR AROMATIC-MOLECULES AB-INITIO Ion Atrazine 3115vn 3115aj Xenon Dipole Atomic data BENZENE MOLECULE Argon Electron correlation Chimie quantique CP violation Pesticide Electron electric dipole moment Coupled cluster calculations Valence bond X-ray spectroscopy 3470+e A priori Localization Wave functions Configuration Interaction Numerical calculations ALGORITHM Density functional theory

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