NONEMPIRICAL WAVE-FUNCTIONS FOR VERY LARGE MOLECULES .2. THE PRDDO M/FCP METHOD/

A variation of the frozen-core potential (FCP) method is developed and implemented within the modified version of the method of partial rete ntion of diatomic differential overlap (PRDDO/M). The explicit treatme nt of core electrons is replaced with a potential based on the actual core-valence integrals rather than upon an arbitrary model potential. The core-valence orthogonality requirement is replaced by an energy sh ift operator. PRDDO/M/FCP calculations exhibit good agreement with ab initio calculations with the same basis set, while reducing the comput ational cost significantly. (C) 1997 John Wiley & Sons, Inc.