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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
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