Two-mode Floquet fewest switches surface hopping for nonadiabatic dynamics driven by two-frequency laser fields

Abstract

Two-frequency (two-color) laser fields provide a powerful and flexible means for steering molecular dynamics. However, quantitatively reliable and scalable theoretical tools for simulating laser-driven nonadiabatic processes under such fields remain limited. Here, we develop a two-mode Floquet fewest switches surface hopping (two-mode F-FSSH) approach for two-frequency driving within a mixed quantum–classical framework. We validate the algorithm on three driven one-dimensional two-state models: a Rabi model and two avoided-crossing scattering models. The electronic and nuclear dynamics are benchmarked against numerically exact results from split-operator calculations, showing good agreement across a broad range of initial conditions and field parameters. These results establish two-mode F-FSSH as a practical framework for designing and simulating two-frequency control protocols and motivate extensions to more realistic systems.