HANDLING OF INTRINSIC DIVERGENCE IN THE ORTHOGONAL GRADIENT-METHOD OF ORBITAL OPTIMIZATION IN AN MC-SCF FRAMEWORK AND GEOMETRY OPTIMIZATION IN PATHOLOGICAL CASES .1. (PROPYNAL IN EXCITED-STATES)

It is demonstrated that a generalized version of the orthogonal gradient method of orbital optimization may sometimes encounter a specific divergence problem which may be termed intrinsic to the first order method. Instead of switching over to a more sophisticated second order method one can cure the divergence problem at the first order level itself by suitably tailoring the MC-SCF operator or the MC-SCF energy matrix. Results of complete geometry optimization of propynal in 1,3npi* and 3pipi* states (pathological cases) are reported to demonstrate the usefulness of the method at an INDO-MCSCF level of approximation. The results of structure calculations are further rationalized from generalized quantum chemical bond order indices.