have to be applied to the GFT formulas ( )- (10), where Q G g is the APC of the g-th nucleus of fragment G. These modified GFT formulas inherit the analogy of the original GFT formulas with the Slater-Condon rules. Hence, we refer to such a variational calculation of the full-system states as "Excitonic Configuration Interaction" (ECI) and to the APC-embedded products as "excitonic Slater determinants" (ESDs). Also, for the sake of brevity, we will refer to the GFT formulas (8), (9), and (10) with modifications (18) as the "ECI formulas". Not to be mistaken by the name, ESDs are not N el × N el SDs, but rather linear combinations of N el × N el SDs, because the APC-embedded site states are linear combinations of the site-specific SDs.