Title: Double spin-flip approach within equation-of-motion coupled cluster and configuration interaction formalisms: Theory, implementation, and examples
Abstract: The spin-flip (SF) approach is extended to excitations that flip the spin of two electrons to describe multiconfigurational M(s)=0 wave functions via high spin quintet references. Equations and implementation of the double SF (2SF) approach within equation-of-motion coupled-cluster (EOM-CC) and configuration interaction (CI) formalisms are presented. The numerical performance of the resulting EOM-2SF-CC and 2SF-CI models is demonstrated by calculations of symmetric dissociation of O-H bonds in water, electronic states of linear H(4), double CC bond-breaking in ethylene, and low-lying states of trimethylenemethyl diradical and 2,4-didehydrometaxylylene tetraradical. The results of active-space variants of 2SF are very close to the more computationally expensive full-space counterparts. An efficient implementation of the active-space approximation of the 2SF-configuration interaction doubles (CID) model termed 2SF-configuration interaction singles (CIS) is also reported. The scaling of 2SF-CIS is only N(4), which allows applications to relatively large molecules.
Publication Year: 2009
Publication Date: 2009-01-27
Language: en
Type: article
Indexed In: ['crossref', 'pubmed']
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Cited By Count: 90
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