index - Méthodes et outils de la chimie quantique Accéder directement au contenu

Derniers dépôts, tout type de documents

Short-range corrections to long-range selected configuration interaction calculations are derived from perturbation theory considerations and applied to harmonium (with two to six electrons for some low-lying states). No fitting to reference data is used, and the method is applicable to ground and excited states. The formulas derived are rigorous when the physical interaction is approached. In this regime, the second-order expression provides a lower bound to the long-range full configuration interaction energy. A long-range/short-range separation of the interaction between electrons at a distance of the order of one atomic unit provides total energies within chemical accuracy, and, for the systems studied, provide better results than short-range density functional approximations.

Continuer la lecture Partager

Electronic resonances are metastable states that can decay by electron loss. They are ubiquitous across various fields of science, such as chemistry, physics, and biology. However, current theoretical and computational models for resonances cannot yet rival the level of accuracy achieved by bound-state methodologies. Here, we generalize selected configuration interaction (SCI) to treat resonances using the complex absorbing potential (CAP) technique. By modifying the selection procedure and the extrapolation protocol of standard SCI, the resulting CAP-SCI method yields resonance positions and widths of full configuration interaction quality. Initial results for the shape resonances of \ce{N2-} and \ce{CO-} reveal the important effect of high-order correlation, which shifts the values obtained with CAP-augmented equation-of-motion coupled-cluster with singles and doubles by more than \SI{0.1}{\eV}. The present CAP-SCI approach represents a cornerstone in the development of highly-accurate methodologies for resonances.

Continuer la lecture Partager

ipie is a Python-based auxiliary-field quantum Monte Carlo (AFQMC) package that has undergone substantial improvements since its initial release [J. Chem. Theory Comput., 2022, 19(1): 109-121]. This paper outlines the improved modularity and new capabilities implemented in ipie. We highlight the ease of incorporating different trial and walker types and the seamless integration of ipie with external libraries. We enable distributed Hamiltonian simulations, allowing for multi-GPU simulations of large systems. This development enabled us to compute the interaction energy of a benzene dimer with 84 electrons and 1512 orbitals, which otherwise would not have fit on a single GPU. We also support GPU-accelerated multi-slater determinant trial wavefunctions [arXiv:2406.08314] to enable efficient and highly accurate simulations of large-scale systems. This allows for near-exact ground state energies of multi-reference clusters, [Cu$_2$O$_2$]$^{2+}$ and [Fe$_2$S$_2$(SCH$_3$)]$^{2-}$. We also describe implementations of free projection AFQMC, finite temperature AFQMC, AFQMC for electron-phonon systems, and automatic differentiation in AFQMC for calculating physical properties. These advancements position ipie as a leading platform for AFQMC research in quantum chemistry, facilitating more complex and ambitious computational method development and their applications.

Continuer la lecture Partager

Hedin's equations provide an elegant route to compute the exact one-body Green's function (or propagator) via the self-consistent iteration of a set of non-linear equations. Its first-order approximation, known as $GW$, corresponds to a resummation of ring diagrams and has shown to be extremely successful in physics and chemistry. Systematic improvement is possible, although challenging, via the introduction of vertex corrections. Considering anomalous propagators and an external pairing potential, we derive a new self-consistent set of closed equations equivalent to the famous Hedin equations but having as a first-order approximation the particle-particle (pp) $T$-matrix approximation where one performs a resummation of the ladder diagrams. This pp version of Hedin's equations offers a way to go systematically beyond the $T$-matrix approximation by accounting for low-order pp vertex corrections.

Continuer la lecture Partager

Sujets

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

Statistiques

Nombre de fichiers déposés

242

Nombre de notices déposées

277