Generalization of Quantum-Trajectory Surface Hopping to Multiple Quantum States

In this work, we present a generalization of the quantum trajectory surface hopping (QTSH) to multiple states and its implementation in the Libra package for nonadiabatic dynamics. In lieu of the ad hoc velocity rescaling used in many trajectory-based surface hopping approaches, QTSH utilizes quantum forces to evolve nuclear degrees of freedom continuously. It also lifts the unphysical constraint of enforcing the total energy conservation at the individual trajectory level and rather conserves the total energy at the trajectory ensemble level. Leveraging our new implementation of the multistate QTSH, we perform a comparative analysis of this method with the conventional fewest switches surface hopping approach. We combine the QTSH and decoherence corrections based on the simplified decay of mixing (SDM) and exact factorization (XF), leading to the QTSH-SDM and QTSH-XF schemes. Using the Holstein, superexchange, and phenol model Hamiltonians, we assess the relative accuracy of the resulting combined schemes in reproducing branching ratios, population, and coherence dynamics for a broad range of initial conditions. We observe that the decoherence correction in QTSH is crucial to improve energy conservation as well as the internal consistency between the population from the quantum probability and active state.