Automated Global Mapping of Minimal Energy Points on Seams of Crossing by the Anharmonic Downward Distortion Following Method: A Case Study of H₂CO

Automated global mapping of minimal energy points on seams of crossing (MSX structures) were performed by using the anharmonic downward distortion following (ADD-following) method, which has previously been applied to the single potential energy surfaces (PESs) to perform automated global reaction route mapping. In this study, the ADD-following is applied to a penalty function based on two PESs of different electronic states. The present approach is effective not only for crossing seams between states with different symmetry but also for conical intersections for states with the same symmetry. Many new MSX structures were discovered on the S(0)/T(1) and S(1)/T(1) crossing seams and the S(0)/S(1) conical intersections of H(2)CO by automated global mapping using the ADD-following method. A possible pathway for dissociation of formaldehyde excited to S(1) at low energy is discussed.