  Nonadiabatic dynamics methods are an essential tool for investigating
photochemical processes. In the context of employing first principles
electronic structure techniques, such simulations can be carried out in a
practical manner using semiclassical trajectory-based methods or wave packet
approaches. While all approaches applicable to first principles simulations are
necessarily approximate, it is commonly thought that wave packet approaches
offer inherent advantages over their semiclassical counterparts in terms of
accuracy, and that this trait simply comes at a higher computational cost. Here
we demonstrate that the mapping approach to surface hopping (MASH), a recently
introduced trajectory-based nonadiabatic dynamics method, can be efficiently
applied in tandem with ab initio electronic structure. Our results even suggest
that MASH may provide more accurate results than on-the-fly wave packet
techniques, all at a much lower computational cost.
