Determination of energy minima and saddle points using multireference configuration interaction methods in combination with reduced gradient following:: The S0 surface of H2CO and the T1 and T2 surfaces of acetylene

The implementation of the reduced gradient following (RGF) method into the COLUMBUS quantum-chemical program system is reported using the newly developed analytic MR-CISD/AQCC gradient feature. By this combination a very useful too] has been developed for general searches of stationary points on ground- and excited-state energy surfaces. This procedure is applied to the S-0 surface of H2CO and the T-1 and T-2 surfaces of acetylene. For H2CO we investigated three minima (formaldehyde, s-trans, and s-cis hydroxycarbene) and five saddle points. For the T, and T. states of acetylene the cis- and trans-minima and the planar and nonplanar saddle points were computed. (C) 2002 Wiley Periodicals, Inc.