FULLY VARIATIONAL OPTIMIZATION OF MODERN VB WAVE-FUNCTIONS USING THE CASVB STRATEGY

We outline the CASVB strategy, which may be used either to generate ve ry compact modern valence bond representations of CASSCF wave function s or to optimize general types of modern VB wave function. A simple al gorithm is presented for the elimination of redundant or constrained, parameters from the appropriate second-order optimization problems. Se lected results for three systems-benzene, the allyl radical, and LiH-a re used to illustrate various ways in which CASVB procedures can be us ed to perform fully variational optimizations of nonorthogonal orbital s and structure coefficients in modern VB wave functions. (C) 1997 Joh n Wiley & Sons, Inc.