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Title: Orbital-optimized opposite-spin scaled second order correlation: An economical method to improve the description of open-shell molecules

Abstract

Coupled cluster methods based on Brueckner orbitals are well-known to resolve the problems of symmetry-breaking and spin-contamination that are often associated with Hartree-Fock orbitals. However their computational cost is large enough to prevent application to large molecules. Here they present a simple approximation where the orbitals are optimized with the mean-field energy plus a correlation energy taken as the opposite-spin component of the second order many-body correlation energy, scaled by an empirically chosen parameter (recommended as 1.2 for general applications). This optimized 2nd order opposite spin (abbreviated as O2) method requires fourth order computation on each orbital iteration. O2 is shown to yield predictions of structure and frequencies for closed shell molecules that are very similar to scaled second order Moller-Plesset methods. However it yields substantial improvements for open shell molecules, where problems with spin-contamination and symmetry breaking are shown to be greatly reduced.

Authors:
;
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
Chemical Sciences Division
OSTI Identifier:
950218
Report Number(s):
LBNL-1644E
Journal ID: ISSN 0021-9606; JCPSA6; TRN: US200910%%122
DOE Contract Number:  
DE-AC02-05CH11231
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics
Country of Publication:
United States
Language:
English
Subject:
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; APPROXIMATIONS; ELECTRON CORRELATION; SPIN; SYMMETRY BREAKING

Citation Formats

Lochan, Rohini C., and Head-Gordon, Martin. Orbital-optimized opposite-spin scaled second order correlation: An economical method to improve the description of open-shell molecules. United States: N. p., 2007. Web. doi:10.1063/1.2718952.
Lochan, Rohini C., & Head-Gordon, Martin. Orbital-optimized opposite-spin scaled second order correlation: An economical method to improve the description of open-shell molecules. United States. doi:10.1063/1.2718952.
Lochan, Rohini C., and Head-Gordon, Martin. Mon . "Orbital-optimized opposite-spin scaled second order correlation: An economical method to improve the description of open-shell molecules". United States. doi:10.1063/1.2718952. https://www.osti.gov/servlets/purl/950218.
@article{osti_950218,
title = {Orbital-optimized opposite-spin scaled second order correlation: An economical method to improve the description of open-shell molecules},
author = {Lochan, Rohini C. and Head-Gordon, Martin},
abstractNote = {Coupled cluster methods based on Brueckner orbitals are well-known to resolve the problems of symmetry-breaking and spin-contamination that are often associated with Hartree-Fock orbitals. However their computational cost is large enough to prevent application to large molecules. Here they present a simple approximation where the orbitals are optimized with the mean-field energy plus a correlation energy taken as the opposite-spin component of the second order many-body correlation energy, scaled by an empirically chosen parameter (recommended as 1.2 for general applications). This optimized 2nd order opposite spin (abbreviated as O2) method requires fourth order computation on each orbital iteration. O2 is shown to yield predictions of structure and frequencies for closed shell molecules that are very similar to scaled second order Moller-Plesset methods. However it yields substantial improvements for open shell molecules, where problems with spin-contamination and symmetry breaking are shown to be greatly reduced.},
doi = {10.1063/1.2718952},
journal = {Journal of Chemical Physics},
number = ,
volume = ,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}