title: Fast vibrational configuration interaction using generalized curvilinear coordinates and self-consistent basis.
abstract: In this paper, we couple a numerical kinetic-energy operator approach to the direct-vibrational self-consistent field (VSCF)/vibrational configuration interaction (VCI) method for the calculation of vibrational anharmonic frequencies. By combining this with fast-VSCF, an efficient direct evaluation of the ab initio potential-energy surface (PES), we introduce a general formalism for the computation of vibrational bound states of molecular systems exhibiting large-amplitude motion such as methyl-group torsion. We validate our approach on an analytical two-dimensional model and apply it to the methanol molecule. We show that curvilinear coordinates lead to a significant improvement in the VSCF/VCI description of the torsional frequency in methanol, even for a simple two-mode coupling expansion of the PES. Moreover, we demonstrate that a curvilinear formulation of the fast-VSCF/VCI scheme improves its speed by a factor of two and its accuracy by a factor of 3.
authors.affiliation: Laboratoire Interdisciplinaire Carnot de Bourgogne, UMR 5209 CNRS, Université de Bourgogne, 9 Av. A. Savary, BP 47870, F-21078 Dijon Cedex, France. yohann.scribano@u-bourgogne.fr
authors.forename: Yohann
authors.initials: Y
authors.lastname: Scribano
authors.forename: David M
authors.initials: DM
authors.lastname: Lauvergnat
authors.forename: David M
authors.initials: DM
authors.lastname: Benoit