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