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 S0 surface of H2CO and the T1 and T2 surfaces of acetylene. For H2CO we investigated three minima (formaldehyde, s-trans, and s-cis hydroxycarbene) and five saddle points. For the T1 and T2 states of acetylene the cis- and trans-minima and the planar and nonplanar saddle points were computed.
- Analytic gradients for excited states
- Reduced gradient following
- Saddle point search