title: An exponential multireference wave-function Ansatz.
abstract: An exponential multireference wave-function Ansatz is formulated. In accordance with the state universal coupled-cluster Ansatz of Jeziorski and Monkhorst [Phys. Rev. A 24, 1668 (1981)] the approach uses a reference specific cluster operator. In order to achieve state selectiveness the excitation- and reference-related amplitude indexing of the state universal Ansatz is replaced by an indexing which is based on excited determinants. There is no reference determinant playing a particular role. The approach is size consistent, coincides with traditional single-reference coupled cluster if applied to a single-reference, and converges to full configuration interaction with an increasing cluster operator excitation level. Initial applications on BeH2, CH2, Li2, and nH2 are reported.
authors.affiliation: Institute for Theoretical Chemistry, University of Cologne, Greinstrasse 4, 50939 Cologne, Germany. michael.hanrath@uni-koeln.de
authors.forename: Michael
authors.initials: M
authors.lastname: Hanrath