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

Published:: Berkeley, Calif. : Lawrence Berkeley National Laboratory, 2007.
Oak Ridge, Tenn. : Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy.
Physical Description:: 41 : digital, PDF file
Additional Creators:: Lawrence Berkeley National Laboratory and United States. Department of Energy. Office of Scientific and Technical Information

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Summary:

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.

Report Numbers:

E 1.99:lbnl-1644e
lbnl-1644e

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Note:

Published through SciTech Connect.
01/01/2007.
"lbnl-1644e"
Journal of Chemical Physics ISSN 0021-9606; JCPSA6 FT
Head-Gordon, Martin; Lochan, Rohini C.
Chemical Sciences Division

Funding Information:

DE-AC02-05CH11231

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