Orbitaloptimized oppositespin scaled second order correlation: An economical method to improve the description of openshell molecules
Abstract
Coupled cluster methods based on Brueckner orbitals are wellknown to resolve the problems of symmetrybreaking and spincontamination that are often associated with HartreeFock 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 meanfield energy plus a correlation energy taken as the oppositespin component of the second order manybody 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 MollerPlesset methods. However it yields substantial improvements for open shell molecules, where problems with spincontamination 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):
 LBNL1644E
Journal ID: ISSN 00219606; JCPSA6; TRN: US200910%%122
 DOE Contract Number:
 DEAC0205CH11231
 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 HeadGordon, Martin. Orbitaloptimized oppositespin scaled second order correlation: An economical method to improve the description of openshell molecules. United States: N. p., 2007.
Web. doi:10.1063/1.2718952.
Lochan, Rohini C., & HeadGordon, Martin. Orbitaloptimized oppositespin scaled second order correlation: An economical method to improve the description of openshell molecules. United States. doi:10.1063/1.2718952.
Lochan, Rohini C., and HeadGordon, Martin. Mon .
"Orbitaloptimized oppositespin scaled second order correlation: An economical method to improve the description of openshell molecules". United States.
doi:10.1063/1.2718952. https://www.osti.gov/servlets/purl/950218.
@article{osti_950218,
title = {Orbitaloptimized oppositespin scaled second order correlation: An economical method to improve the description of openshell molecules},
author = {Lochan, Rohini C. and HeadGordon, Martin},
abstractNote = {Coupled cluster methods based on Brueckner orbitals are wellknown to resolve the problems of symmetrybreaking and spincontamination that are often associated with HartreeFock 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 meanfield energy plus a correlation energy taken as the oppositespin component of the second order manybody 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 MollerPlesset methods. However it yields substantial improvements for open shell molecules, where problems with spincontamination 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}
}

The performance of correlated optimized effective potential (OEP) functionals based on the spinresolved secondorder correlation energy is analysed. The relative importance of singly and doubly excited contributions as well as the effect of scaling the same and opposite spin components is investigated in detail comparing OEP results with Kohn–Sham (KS) quantities determined via an inversion procedure using accurate ab initio electronic densities. Special attention is dedicated in particular to the recently proposed scaledopposite–spin OEP functional [I. Grabowski, E. Fabiano, and F. Della Sala, Phys. Rev. B 87, 075103 (2013)] which is the most advantageous from a computational point of view.more »

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