A RAPID GENERALIZED VALENCE-BOND ALGORITHM FOR SEMIEMPIRICAL NDDO CALCULATIONS

A recently developed algorithm based on the coupled cluster ansatz for the generalized valence-bond perfect-pairing model is adapted for the NDDO class of semiempirical methods. It allows for the calculation of the nondynamic electron correlation and executes as rapidly as the semiempirical molecular orbital method. To assess the interplay of the nondynamic and dynamic electron correlation vs. parameterization, preliminary results are presented for rotation about a double bond, dissociations about single bonds, and the relative stabilities of biradical isomers. (C) 1995 John Wiley & Sons, Inc.