The two exceptions were MnP(O 2 ), a notoriously challenging system with a low-lying sextet, and MnP(O), which DLPNO-CCSD(T) predicts to have a quartet less than 1 kcal/mol higher than the ground state doublet. For both of these systems, the six tested functionals were evenly split in their spin assignments, which highlights the difficulty that the Mn porphyrins pose for spin state ordering. Overall, these results show that outside of some exceptional cases, application of several functionals with a range of exact exchange can be a viable approach to determine ground state spins for metalloporphyrins when experimental data or higher-level calculations are unavailable or unfeasible. Since the difficulty of ground state spin ordering arises largely because these systems have small spin splitting energies, one might assume that the energetic consequences of misassigning the ground state multiplicity would be rather small. Within our data set, when a functional incorrectly predicted the ground state, the true ground state was only 5.4 kcal/mol higher in energy than the incorrect state, on average (median 3.9 kcal/mol). To properly assess the impact of these spin splitting energies, we recalculated the LFESR for the best-performing B3LYP using the ground state spins determined by Baran et al. in a previous study using the pure GGA OLYP (See Table ). by roughly 0.4 eV while the remaining species are largely unchanged. Thus, while the average spin splitting energies for the metalloporphyrins are quite small, it only takes the reversal of spin ordering (or the use of an erroneous ground state spin calculated at a lower level theory) for a single larger gap intermediate to greatly impact theoretical overpotentials.