FIG. : Potential energy surfaces of the S0 and S1 states of PSB3 calculated at SF-BH&HLYP/6-31G* level of theory. Energies are measured relative to the S0 energy at the MECP structure, which is taken as the coordinate origin. This plot exhibits the correct double-cone topology around the CX, whereas the analogous plot at the CIS level (Fig. ) does not.