A Multiband Semiclassical Model for Surface Hopping Quantum Dynamics

In the paper we derive a semiclassical model for surface hopping allowing quantum dynamical nonadiabatic transition between different potential energy surfaces in which cases the classical Born--Oppenheimer approximation breaks down. The model is derived using the Wigner transform and Weyl quantization, and the central idea is to evolve the entire Wigner matrix rather than just the diagonal entries as was done previously in the adiabatic case. The off-diagonal entries of the Wigner matrix suitably describe the nonadiabatic transition, such as the Berry connection, for avoided crossings. We study the numerical approximation issues of the model, and then conduct numerical experiments to validate the model.