title: A companion perturbation theory for state-specific multireference coupled cluster methods.
abstract: A partitioning scheme is applied to the state-specific Mukherjee multireference coupled cluster method to derive a companion perturbation theory (Mk-MRPT2). A production-level implementation of Mk-MRPT2 is reported. The effectiveness of the Mk-MRPT2 method is demonstrated by application to the classic F(2) dissociation problem and the lowest-lying electronic states of meta-benzyne, including computations with up to 766 atomic orbitals. We show that Mk-MRPT2 theory is particularly useful in multireference focal point extrapolations to determine ab initio limits.
authors.affiliation: Center for Computational Chemistry and Department of Chemistry, University of Georgia, Athens, GA 30602, USA.
authors.forename: Francesco A
authors.initials: FA
authors.lastname: Evangelista
authors.forename: Andrew C
authors.initials: AC
authors.lastname: Simmonett
authors.forename: Henry F
authors.initials: HF
authors.lastname: Schaefer
authors.forename: Debashis
authors.initials: D
authors.lastname: Mukherjee
authors.forename: Wesley D
authors.initials: WD
authors.lastname: Allen