The DVS-APC active space for [Cr(CN) 6 ] 3-is also qualitatively identical to previous results. Although the previous CASPT2 study of [Cr(CN) 6 ] 3-makes use of a number of unique active spaces, these all include some combination of the valence d orbitals and the σ, π, and π * ligand orbitals. As shown in Figure , the DVS-APC-selected active space is a (9,13) including the three doubly occupied ligand orbitals, three singly occupied d orbitals, two unoccupied d orbitals, and 6 unoccupied ligand orbitals.