When describing the interaction of a molecule with (classical) light, as in the case of a laser pulse or a continuous-wave laser , an additional time-dependent term may appear in the Hamiltonian, which can be expressed as V (r, R,t) =μ(r, R) • E(t) in the dipole approximation. In this case, the interaction potential V (r, R,t) depends on μ(r, R), the molecule electric dipole moment, and on E(t), the external time-dependent electric field. In some situations , the relativistic correction due to the geometrydependent spin-orbit coupling ĤSOC (x, R) can be included in the system Hamiltonian, where the variable x = [r, σ] accounts for the electronic spin σ as well as for the electronic positions r.