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

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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 ... continued below

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Lochan, Rohini C. & Head-Gordon, Martin January 1, 2007.

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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.

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  • Journal Name: Journal of Chemical Physics

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  • Report No.: LBNL-1644E
  • Grant Number: DE-AC02-05CH11231
  • Office of Scientific & Technical Information Report Number: 950218
  • Archival Resource Key: ark:/67531/metadc927793

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  • January 1, 2007

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  • Nov. 13, 2016, 7:26 p.m.

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  • Nov. 18, 2016, 3:05 p.m.

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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, article, January 1, 2007; Berkeley, California. (digital.library.unt.edu/ark:/67531/metadc927793/: accessed November 19, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.