Continuing our pursuit of accurate electronic structure treatment for multi-metallic nodes, we have studied the spin-state ordering of the mixed valence [Fe III Fe III Fe II (µ 3 -O)-(HCOO) 6 ] system, abbreviated as Fe 3 and depicted in Fig. . We show that LASSIS and LASSIS-PDFT offer significant advantages and robustness compared to the previously reported LASSI method, leading to quantitatively improved results. We performed calculations with small (all 3d orbitals on all Fe atoms) and large (all 3d & 3d ′ orbitals on all Fe) active spaces, corresponding to (16, 15) and (16, 30) active spaces, respectively. Using LASSCF, we optimized the orbitals for the high-spin state (S=7, M S =7). The optimized orbitals with their occupancies are depicted in SI Tables and.