The hierarchical expansion of the kinetic energy operator in curvilinear coordinates extended to the vibrational configuration interaction method.

The hierarchical expansion of the kinetic energy operator in curvilinear coordinates presented earlier for the vibrational self-consistent field technique is extended to the vibrational configuration interaction (VCI) method. The high accuracy of the modified VCI method is demonstrated by computing first excitation energies of the H(2)O(2) molecule using an analytic potential (PCPSDE) and showing convergence to accurate results from full dimensional discrete variable representation calculations.