In contrast, invariant metrics do not depend on the choice of MOs and these are the only metrics that can be interpreted as genuine physical properties of the excitonic wave function. Perhaps the simplest such property is d e-h , the mean electronhole separation, but the present data set contains various centrosymmetric molecules for which d e-h = 0. Even for molecules lacking inversion symmetry, typical values of d e-h for localized valence excitations (d e-h 1.5 Å, with most values < 1 Å) are not that much different from values obtained for Rydberg excitations (d e-h < 2 Å); see Fig. . For these reasons, we discount d e-h as a diagnostic for CT character although it remains a physically interpretable measure of electron-hole separation.