to model a set of relevant vibrations. Here, b † i and bi are bosonic creation and annihilation operators with respect to a basis of local oscillators (i.e., b † i creates a vibrational quantum for the i-th local oscillator). The above vibrational exciton Hamiltonian contains as parameters the harmonic frequencies of the local oscillators, ωi , the anharmonic shifts ∆ i of these local oscillators, as well as the couplings J ij between local oscillators. For these parameters, one applies an empirical model (vibrational frequency map), in which the local harmonic frequencies as well as coupling constants are parametrized in terms of the molecular structure and the electric field at the local oscillators. The anharmonic shift is commonly modeled using a fixed value.