Here, we only consider the model by Torii and Tasumi , in which r ij is a vector pointing from one peptide unit to the other (using a suitable definition of the center of each peptide group in terms of the atomic positions of the C, O, N, and H atoms), and where µ i and µ j are local transition dipole moments, for which another parametrization in terms of the geometry of the peptide group is used.