In semiclassical methods, the electronic wave functions may also be considered to be functions of time (t) because (2) where r denotes the electronic coordinates, and R(t) is the trajectory of nuclear motion. A popular semiclassical method is trajectory surface hopping (TSH). In TSH one only requires the NAC in the direction of the current velocity, 𝐑 ̇, because the semiclassical equations only require the time derivative coupling (TDC):