A major simplicity afforded by the FSSH method is that the derivative coupling vectors d ab (R) are not explicitly required as the nuclear forces (unlike in the mean-field EH method) do not require this quantity for time-evolution (except at the hops for rescaling), and the electronic propagation only requires the scalar non-adiabatic coupling terms d ab • dR/dt = ⟨Ψ a |d/dt|Ψ b ⟩, which can be easily obtained via finite difference wavefunction overlaps of the polaritonic states throughout the trajectory. This procedure is immensely cheaper than the direct computation of the non-adiabatic coupling vectors themselves, wherein one only needs to compute the non-adiabatic coupling vectors to rescale the nuclei at the moment of a hop. Or, one can ignore the asymmetric nuclear velocity rescaling altogether and perform uniform energy-based rescaling, which is known to provide slightly worse dynamics but alleviates the computation of the vector non-adiabatic coupling altogether.