Employing ECISD+FDA level in MgG 2+ 4 reduces the RMSD of the energies by nearly a factor of two, compared to ECIS+FDA (from 0.6-0.8 eV to 0.2-0.4 eV). This is because including DLE products mitigates one source of non-size extensivity of ECIS+FDA-the non-complete ECI expansion. Furthermore, they account for residual excitonic correlation in the excited fullsystem states that is missed by ECIS+FDA. As can be seen in Table , all excited full-system states have contributions of DLE products of about 4-6% (E 2 in the table). These mostly come from 0 F S 1 ,GS 1 , 0 F S 1 ,GS 3 and 0 F S 3 ,GS 3 ESDs, corresponding to the DLEs on each pair of guanines (guanine indices F and G being any two different numbers between 1 and 4). We note that, although the energies were improved by adding DLE products, the oscillator strengths did not change significantly, because the DLE products do not contribute to the transition dipole moments from the state dominated by the GS product.