Ab initio calculation for the fundamental frequencies of H₂O

Abstract

The question of the best method to determine frequencies of triatomic molecules by entirely ab initio methods is discussed, with reference to H₂O. MCSCF-CI calculations are reported at selected geometries, and have been used to generate a potential surface from which the vibrational energies are calculated by a variational method. The calculated fundamental frequencies are in error by 28 cm^-1 (bend), and 10 cm^-1 and 4 cm^-1 (symmetric and asymmetric stretch).