A new analytic form of ab initio potential energy function:: An application to H2O

The potential energy function (PEF) for H2O has been generated by the modified Shepard interpolation method using the fourth-order Taylor expansion at the MP2/aug-cc-pVTZ level. The reference points for the interpolation have been set at only three points, i.e., the equilibrium structure plus two symmetrically equivalent points in the coupling region of OH symmetric and antisymmetric stretching modes. The vibrational self-consistent field (VSCF) and virtual configuration interaction (VCI) methods have been applied to determine fundamentals, overtones, and combination bands of H2O. The mean absolute deviation over these energy levels from the corresponding ones determined by the direct VCI method is only 4.8 cm(-1). (C) 2002 American Institute of Physics.