where Ω is a diagonal matrix with the normal-mode vibrational energies hω p of the considered normal modes on its diagonal. By construction, the diagonalization of this coupling matrix recovers the original normal modes as well as the corresponding vibrational energies and frequencies. Here, we postulate that the matrix H exciton underlying vibrational exciton models and the coupling matrix Ω that is accessible from quantum-chemical calculations via a localization of normal modes, are identical, i.e.,