title: Non-orthogonal configuration interaction for the calculation of multielectron excited states.
abstract: We apply Non-orthogonal Configuration Interaction (NOCI) to molecular systems where multielectron excitations, in this case double excitations, play a substantial role: the linear polyenes and β-carotene. We demonstrate that NOCI when applied to systems with extended conjugation, provides a qualitatively correct wavefunction at a fraction of the cost of many other multireference treatments. We also present a new extension to this method allowing for purification of higher-order spin states by utilizing Generalized Hartree-Fock Slater determinants and the details for computing ⟨S(2)⟩ for the ground and excited states.
authors.affiliation: Department of Chemistry, University of California Berkeley, Berkeley, California 94720, USA and Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: Eric J
authors.initials: EJ
authors.lastname: Sundstrom
authors.affiliation: Department of Chemistry, University of California Berkeley, Berkeley, California 94720, USA and Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
authors.forename: Martin
authors.initials: M
authors.lastname: Head-Gordon