We also examined the topography around the CXs, which is believed to have correlations with the efficiency of nonadiabatic transitions. Here, we only consider MECP(C 2 C 3 ) because most of the nonadiabatic S 1 → S 0 transitions in NMD simulations discussed below occur near this particular CX. Yarkony 67 has introduced several parameters that characterize the topography of a CX. Denoting the lengths of the branching-plane vectors introduced in Section II A as g = g and h = h , these topographical parameters include FIG. : Critical-point structures of PSB3 including S0 and S1 minima and the S1/S0 MECP, optimized using SF-BH&HLYP (geometric parameters in bold), LR-ωB97X/TDA (parameters in plain font), and LR-ωB97X (parameters in italics). The bond lengths (in Ångstroms) are labeled in black and the twist angles (in degrees) are in red. MECP geometries were not optimized using full LR-TDDFT but rather only with the TDA, due to triplet instability problems.