Given the set of site states, the ECIS basis (for both systems) initially contains 65 ESDs-one GS product and 16 (seven singlet and 3×3 triplet excitations) LE products per guanine fragment. In ECISD, additionally 16 2 DLE products for each of the six pairs of guanines are included, for a total of 1601 ESDs. After applying the overlap criterion (Equation ( )) to the initial ECI basis, all ESDs containing the 1 πRy 6 stateregardless of system, embedding, or excitation rank-are expelled. This is expected because, as discussed, the lobes of the 1 πRy 6 state penetrate the region of the neighboring fragment, leading to a violation of the SOA. The 1 πRy 6 state is only present in the FDA calculation of G 4 and the FDA and ESP calculations of MgG 2+ 4 . Hence, these calculations were effectively performed with one less singlet state, leading to the numbers of ESDs and ECSFs labeled as "7S+3T" in Table . In particular, in the ECIS calculations without 1 πRy 6 , only 61 ESDs are obtained (before considering spin), while in the ECISD calculation 1411 ESDs were found. In the ESP and EHF calculations of G 4 and the EHF calculation of MgG 2+ 4 , the problematic 1 πRy 6 state is not part of the site state set, and no ESDs had to be expelled from the excitonic basis due to SOA violations. Thus, these calculations were performed with the basis denoted as "8S+3T" in Table (65 ESDs for ECIS and 1601 for ECISD).