The [2Fe-2S] dimers are key biological molecules. Due to their large number of low-lying electronic and magnetic states, they play a crucial role in nitrogen fixation, electron transfer processes, and redox chemistry. Additionally, they serve as model systems for understanding the chemistry of larger iron-sulfur clusters. In this study we have examined the energetics of the low-lying spin-states for [Fe 2 S 2 (SCH 3 ) 4 ] 2-and [Fe 2 S 2 (SCH 3 ) 4 ] 3-(also denoted as, [2Fe-2S] 2-/3-), depicted in Fig. , that mimic the iron-sulfur motifs found in ferrodoxins. The former is in the oxidized state with both iron centers as Fe III , while the latter complex is a mixed valence complex where the iron centers are in Fe II and Fe III oxidation states. For complexes [2Fe-2S] 2-and [2Fe-2S] 3-, we have used the 3d and 3d ′ subshells in the active space, i.e. (10, 20) and (11, 20) active space respectively. This active space was divided into two fragments, where each fragment corresponds to a single Fe atom. The LASSCF method with AVAS 37 initial guess was used to optimize the orbitals for the highspin states, with S=5, M S =5 for [2Fe-2S] 2-and S= , M S = 9 2 for [2Fe-2S] 3-. Using and DMRG-PDFT, we have calculated the reference values of spin-state gaps in the same active space and orbitals using a bond-dimension value (M) of 1000. The relative energies of both complexes are shown in Table , and the absolute values are included in Table of the SI. The optimized LASSCF orbitals for the two molecules are depicted with their occupancies in Tables and of the SI.