Mixed quantum-classical equilibrium in global flux surface hopping

Global flux surface hopping (GFSH) generalizes fewest switches surface hopping (FSSH)-one of the most popular approaches to nonadiabatic molecular dynamics-for processes exhibiting superexchange. We show that GFSH satisfies detailed balance and leads to thermodynamic equilibrium with accuracy similar to FSSH. This feature is particularly important when studying electron-vibrational relaxation and phonon-assisted transport. By studying the dynamics in a three-level quantum system coupled to a classical atom in contact with a classical bath, we demonstrate that both FSSH and GFSH achieve the Boltzmann state populations. Thermal equilibrium is attained significantly faster with GFSH, since it accurately represents the superexchange process. GFSH converges closer to the Boltzmann averages than FSSH and exhibits significantly smaller statistical errors. (C) 2015 AIP Publishing LLC.