Here, b † i and bi are bosonic creation and annihilation operators with respect to a local-mode basis, such as the L-VSCF modals (i.e., b † i creates a vibrational quantum for the i-th L-VSCF modal). The exciton Hamiltonian contains as parameters the local-mode harmonic frequencies, ωi , the harmonic coupling constants J ij , and the local-mode anharmonic shifts