The LVC Hamiltonian 74-81 has an analytical form, which (i) approximates harmonically the coupled (diabatic) PESs in the vicinity of the Franck-Condon (FC) region (ii) including linear terms and (iii) coupling linearly the potentials associated to different electronic states. The LVC Hamiltonian is constructed in the diabatic representation, thus the electronic Hamiltonian is not diagonal in this basis, and the used nuclear modes are the normal modes q identified from the harmonic analysis of the ground-state PES in the FC region. The working "molecular" Hamiltonian is ĤLVC (q) = Ĥ(0) (q) + Ŵ 0 (q) + Ŵ 1 (q), (