Analysis of the Karplus-Kolker approximation to Hartree-Fock perturbation theory

<div> <div> <div> <p>Psi4 is a free and open-source ab initio electronic structure program providing Hartree–Fock, density functional theory, many-body perturbation theory, configuration interaction, density cumulant theory, symmetry-adapted perturbation theory, and coupled-cluster theory. Most of the methods are quite efficient thanks to density fitting and multi-core parallelism. The program is a hybrid of C++ and Python, and calculations may be run with very simple text files or using the Python API, facilitating post-processing and complex workflows; method developers also have access to most of Psi4’s core functionality via Python. Job specification may be passed using The Molecular Sciences Software Institute (MolSSI) QCSchema data format, facilitating interoperability. A rewrite of our top-level computation driver, and concomitant adoption of the MolSSI QCArchive Infrastructure project, make the latest version of Psi4 well suited to distributed computation of large numbers of independent tasks. The project has fostered the development of independent software components that may be reused in other quantum chemistry programs. </p> </div> </div> </div>

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Orthogonality-constrained Hartree–Fock and perturbation theory for high-spin open-shell excited states

Péter R. Surján - Highlights in Theoretical Chemistry ◽

10.1007/978-3-662-49825-5_23 ◽

2015 ◽

pp. 189-197

Author(s):

V. N. Glushkov ◽

X. Assfeld

Keyword(s):

Perturbation Theory ◽

Excited States ◽

High Spin ◽

Open Shell ◽

Hartree Fock

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Second-Order Perturbation Theory with Spin-Symmetry-Projected Hartree–Fock

Journal of Chemical Theory and Computation ◽

10.1021/acs.jctc.9b00897 ◽

2019 ◽

Vol 15 (12) ◽

pp. 6688-6702 ◽

Cited By ~ 5

Author(s):

Takashi Tsuchimochi ◽

Seiichiro L. Ten-no

Keyword(s):

Perturbation Theory ◽

Spin Symmetry ◽

Second Order ◽

Order Perturbation ◽

Order Perturbation Theory ◽

Hartree Fock ◽

Second Order Perturbation Theory

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Perturbation theory of short-range atomic interactions

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1970.0130 ◽

1970 ◽

Vol 317 (1531) ◽

pp. 545-574 ◽

Cited By ~ 42

Keyword(s):

Perturbation Theory ◽

Short Range ◽

Similarity Transformation ◽

Order Theory ◽

First Order ◽

Hartree Fock ◽

First Order Theory ◽

Atomic Interactions ◽

Cusp Conditions ◽

Molecular Calculations

A new united atom perturbation theory of the interaction of two atoms at small separations is described. The key feature is a similarity transformation of the Schrödinger equation which enables the cusp conditions to be satisfied at both nuclei and preserves the correct molecular symmetry. The first-order theory is examined in detail and compared with other united atom theories. Numerical calculations are presented for the ground states of the systems H + 2 , HeH 2+ HeH, He 2 and Li + He, based mainly on Hartree-Fock wavefunctions for the united atoms, and are compared with accurate molecular calculations. The agreement is remarkably good for separations up to 1 bohr.

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