State Tracking in Nonadiabatic Molecular Dynamics Using Only Forces and Energies.

A new algorithm for the identification of unavoided (trivial) crossings in nonadiabatic molecular dynamics calculations is reported. The approach does not require knowledge of wave functions or wave function time overlaps and uses only information on state energies and gradients. In addition, a simple phase consistency correction algorithm for time-derivative nonadiabatic couplings is proposed for situations in which wave function time overlaps are not available. The performance of the two algorithms is demonstrated using several state crossing models. The approaches work best for systems with localized nonadiabatic coupling regions but may have difficulties for those with extended regions of nonadiabatic coupling. It is found that state tracking alone is not sufficient for producing correct population dynamics and that nonadiabatic coupling phase correction is required.