On the other hand, in the mixed-valence complex [2Fe-2S] 3-, the additional electron is delocalized between the two Fe centers. Therefore, along with the Heisenberg exchange, double exchange also comes into play, which reduces the gap between high (S= 2 ) and low spin (S= 2 ) to 747.2 and 1284.1 cm -1 respectively at LASSIS and -PDFT level, compared to its oxidized counterpart. All of the methods predict a doublet ground state. The disagreements between the LASSIS and DMRG gaps are similar in magnitude to the [2Fe-2S] 2-case, which corresponds to a greater relative disagreement of up to 20% due to the smaller magnitude of the gaps themselves. However, in this case, LASSIS-PDFT and DMRG-PDFT agree more closely with each other in relative terms (and even in absolute terms in the doublet-octet and doublet-decuplet cases) than LASSIS and DMRG.