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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

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

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