title: Communication: an inexpensive, variational, almost black-box, almost size-consistent correction to configuration interaction singles for valence excited states.
abstract: Configuration interaction singles (CIS) describe excited electronic states only qualitatively and improvements are imperative as a means of recovering chemical accuracy. In particular, variational improvements would be ideal to account for state crossings and electronic relaxation. To accomplish such an objective, in this communication we present a new suite of algorithms, abbreviated VOO-CIS for variationally orbital optimized CIS. We show below that VOO-CIS yields a uniform improvement to CIS, rebalancing the energies of CT states versus non-CT states within the same framework. Furthermore, VOO-CIS finds energetic corrections for CT states that are even larger than those predicted by CIS(D). The computational cost of VOO-CIS depends strongly on the number of excited states requested (n), but otherwise should be proportional to the cost of CIS itself.
authors.affiliation: Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
authors.forename: Xinle
authors.initials: X
authors.lastname: Liu
authors.forename: Qi
authors.initials: Q
authors.lastname: Ou
authors.forename: Ethan
authors.initials: E
authors.lastname: Alguire
authors.forename: Joseph E
authors.initials: JE
authors.lastname: Subotnik