Determination of Energy Minima and Saddle Points Using Multireference Configuration Interaction Methods in Combination with Reduced Gradient Following: The S_O Surface of H_2CO and the T_1 and T_2 Surfaces of Acetylene

摘要

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 tool has been developed for general searches of stationary points on ground- and excited-state energy surfaces. This procedure is applied to the S_O surface of H_2CO and the T_1 and T_2 surfaces of acetylene. For H_2CO we investigated three minima (formaldehyde, s-trans, and s-cis hydroxycarbene) and five saddle points. For the T_1 and T_2 states of acetylene the cis- and trans-minima and the planar and nonplanar saddle points were computed.