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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.

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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.

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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.

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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.

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Sujets

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

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278