In the late 1970’s Meyer and Miller (MM) [J. Chem.
3214 (1979)] presented a classical Hamiltonian corresponding to
a finite set of electronic states of a molecular system (i.e.,
the various potential energy surfaces and their couplings), so
that classical trajectory simulations could be carried out
treating the nuclear and electronic degrees of freedom (DOF) in
an equivalent dynamical framework (i.e., by classical
mechanics), thereby describing non-adiabatic dynamics in a more