On the evaluation of spin-orbit coupling matrix elements in a spin-adapted basis

In the present article, we outline a simple scheme for generating configuration interaction matrix elements for spin-orbit interactions in molecules. The procedure leads to a close parallelism with spin-free permutation-group approaches. Unitary shift operators were successfully used on the orbital space to generate the matching permutations necessary to evaluate the required matrix elements. The procedure is adequately illustrated using examples. (C) 1999 John Wiley & Sons, Inc.