title: Simple and accurate method to evaluate tunneling splitting in polyatomic molecules.
abstract: A practical and accurate semiclassical method for calculating the tunneling splitting of the ground state in polyatomic molecules is presented based on a recent version of the instanton theory [J. Chem. Phys. 115, 6881 (2001)]. The method uses ab initio quantum chemical data for the potential energy surface without any concomitant extrapolation and requires only a small number of ab initio data points to get convergence even for large molecules. This enables one to use an advanced level of electronic structure theory and achieve a high accuracy of the result. The method is applied to the 9-atomic malonaldehyde molecule by making use of the potential energy surface at the level of CCSD(T) with the hybrid basis set of aug-cc-pVTZ (for oxygen atoms and the transferred hydrogen atom) and cc-pVTZ (for other atoms).
authors.affiliation: Department of Theoretical Studies, Institute for Molecular Science, Myodaiji, Okazaki 444-8585, Japan. gena@ims.ac.jp
authors.forename: Gennady V
authors.initials: GV
authors.lastname: Mil'nikov
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Yagi
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Taketsugu
authors.forename: Hiroki
authors.initials: H
authors.lastname: Nakamura
authors.forename: Kimihiko
authors.initials: K
authors.lastname: Hirao