The first step in an excitonic calculation is the computation of the site states. At the Franck-Condon geometries of G 4 and MgG 4 , all guanine sites are symmetry equivalent, so that in this section it is sufficient to discuss the site states of one guanine moiety. The vertical excitation energies and state characters are presented in Figure , for both systems and the three different embedding schemes (FDA, ESP, EHF). Table contains the corresponding excitation energies and oscillator strengths, while Table contains the approximate (qualitative) expansions of the site states in the terms of MO excitations. Figure displays all MOs needed to define the characters of the site states.