Trajectory surface hopping molecular dynamics simulation by spin-flip time-dependent density functional theory.

This paper presents the nonadiabatic molecular dynamics simulation combined with the spin-flip time-dependent density functional theory (SF-TDDFT). In contrast to the conventional single-reference electronic structure methods, which have difficulty in describing the S/S conical intersections, the SF-TDDFT can yield the correct topology of crossing points. Thus, one expects that the method can take naturally into account the S → S nonadiabatic transitions. We adopt Tully's fewest switch surface hopping algorithm by introducing the analytic SF-TDDFT nonadiabatic coupling vector. We apply the proposed method to the photoisomerization reactions of E-azomethane, methanimine, and ethene molecules and reproduce the results of previous studies based on the multireference methods. The proposed approach overcomes the ad hoc treatment of S → S transition at the single-reference calculation level and affords both the dynamics on the S state and the recovery of the S state with modest computational costs.