Here, we will explore a third strategy, which exploits the connection between the L-VCISD matrix and the vibrational exciton Hamiltonian. To this end, we use the frequencies of the L-VSCF eigenstates (i.e., the diagonal elements of the L-VCISD matrix) on the diagonal of the vibrational exciton Hamiltonian ("L-VSCF exciton model"). This way, the anharmonicity is taken into account directly and no empirical anharmonic shift is required.