Perturbative inversion of the HOCl potential energy surface via singular value decomposition

A global, ab initio potential energy surface for HOCl [K.A. Peterson, S. Skokov, J.M. Bowman, J. Chem. Phys. (in press)] is corrected to exactly reproduce experimental vibrational energies for 22 known bound states, and rotational constants for 9 low-energy states. The ab initio potential is first `morphedʹ by means of coordinate scaling to substantially improve its accuracy. Then a small correction potential is determined by the inverse perturbation theory via the singular value decomposition method [Q. Wu, J.Z.H. Zhang, Chem. Phys. Lett. 252 (1996) 195]. The correction potential, expanded in the truncated basis set of distributed gaussian functions, is an analytical function of the coordinates, and yields results that are within 0.14 cm−1 of the experimental energies.