in eq. ( ) in contrast to our earlier definition of "fraction of transition density matrix" (FTDM). Further, to judge on exciton localization we analyze how the largest (or "highest", H) diagonal element F H changes with time. The ensemble-averaged F H as a function of time is presented in Fig. . Importantly, the CIS and CISD F H (t) curves are similar. Both show the rise of F H with a localization time constant (τ loc ) of ∼50 fs (see Tab. 1) which was obtained using an exponential fit of the form