title: Vibrational excitation energies from vibrational coupled cluster response theory.
abstract: Response theory in the context of vibrational coupled cluster (VCC) theory is introduced and used to obtain vibrational excitation energies. The relation to the vibrational configuration interaction (VCI) approach is described, and the increase in accuracy of VCC response energies relative to VCI energies is discussed theoretically in terms of a perturbational order expansion and demonstrated numerically. To illustrate the theory, a pilot implementation is used to obtain anharmonic vibrational frequencies for fundamental, first overtone and combination excitations of formaldehyde as well as for the fundamental transitions of ethylene.
authors.affiliation: The Lundbeck Foundation Center for Theoretical Chemistry, Department of Chemistry, University of Aarhus, Langelandsgade 140, DK-8000 Aarhus C, Denmark. seidler@chem.au.dk
authors.forename: Peter
authors.initials: P
authors.lastname: Seidler
authors.forename: Ove
authors.initials: O
authors.lastname: Christiansen