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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
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