title: Bridging single and multireference coupled cluster theories with universal state selective formalism.
abstract: The universal state selective (USS) multireference approach is used to construct new energy functionals which offer a possibility of bridging single and multireference coupled cluster theories (SR/MRCC). These functionals, which can be used to develop iterative and non-iterative approaches, utilize a special form of the trial wavefunctions, which assure additive separability (or size-consistency) of the USS energies in the non-interacting subsystem limit. When the USS formalism is combined with approximate SRCC theories, the resulting formalism can be viewed as a size-consistent version of the method of moments of coupled cluster equations employing a MRCC trial wavefunction. Special cases of the USS formulations, which utilize single reference state specific CC [V. V. Ivanov, D. I. Lyakh, and L. Adamowicz, Phys. Chem. Chem. Phys. 11, 2355 (2009)] and tailored CC [T. Kinoshita, O. Hino, and R. J. Bartlett, J. Chem. Phys. 123, 074106 (2005)] expansions are also discussed.
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: Karol
authors.initials: K
authors.lastname: Kowalski