An approximate variational perturbation model for molecular energy

A variational procedure is applied to the perturbation treatment of the configuration interaction matrix of Diner, Malrieu, and Claverie (PCILO) to yield a method that appears to better reproduce the exact energy surface for small molecules. In addition, many points on the potential energy surface can be searched with N 2 steps, where N is the number of basis orbitals, until the region of interest is uncovered. The procedure then becomes competitive in execution time with semiclassical methods used in examining large molecules. The implications of applying this variational procedure for large molecules arc discussed.