title: Implementation of the multireference Brillouin-Wigner and Mukherjee's coupled cluster methods with non-iterative triple excitations utilizing reference-level parallelism.
abstract: In this paper we discuss the performance of the non-iterative state-specific multireference coupled cluster (SS-MRCC) methods accounting for the effect of triply excited cluster amplitudes. The corrections to the Brillouin-Wigner and Mukherjee's MRCC models based on the manifold of singly and doubly excited cluster amplitudes (BW-MRCCSD and Mk-MRCCSD, respectively) are tested and compared with exact full configuration interaction results for small systems (H(2)O, N(2), and Be(3)). For the larger systems (naphthyne isomers) the BW-MRCC and Mk-MRCC methods with iterative singles, doubles, and non-iterative triples (BW-MRCCSD(T) and Mk-MRCCSD(T)) are compared against the results obtained with single reference coupled cluster methods. We also report on the parallel performance of the non-iterative implementations based on the use of processor groups.
authors.affiliation: William R. Wiley Environmental Molecular Sciences Laboratory, Battelle, Pacific Northwest National Laboratory, K8-91, P.O. Box 999, Richland, Washington 99352, USA.
authors.forename: Kiran
authors.initials: K
authors.lastname: Bhaskaran-Nair
authors.forename: Jiří
authors.initials: J
authors.lastname: Brabec
authors.forename: Edoardo
authors.initials: E
authors.lastname: Aprà
authors.forename: Hubertus J J
authors.initials: HJ
authors.lastname: van Dam
authors.forename: Jiří
authors.initials: J
authors.lastname: Pittner
authors.forename: Karol
authors.initials: K
authors.lastname: Kowalski