that we obtain for each of the combinations of active space and basis set for all 3237 wave functions that we converged. As expected, we find that the SA-CASSCF error increases when we move from a larger to a smaller basis set with a given active space scheme or when we move from a larger active space to a smaller one with a given basis set. However, in order to reasonably evaluate the accuracies of these methods, we need to eliminate results whose error is driven mainly by poorly chosen active spaces. To analyze only cases with reasonable active spaces we set a threshold T on the SA-CASSCF error of 1.1 eV (T SA-CASSCF = 1.1 eV). That is, we consider that the APC scheme has produced a good active space if the error in the SA-CASSCF excitation energy is less than 1.1 eV. Figure shows the performance of SA-CASSCF, tPBE, tPBE0, and NEVPT2 at different active space and basis set sizes after using the 1.1 eV SA-CASSCF error cutoff to eliminate poor active space choices. As expected, instead of observing an increasingly poor performance for SA-CASSCF excitations as active space and basis set size is decreased, we instead see a consistent error of roughly 0.39 ± 0.03 eV with an increasing amount of excitations excluded by T SA-CASSCF = 1.1 eV. Of course, with a better automatic active space selection scheme one would observe an increased amount of excitations included at each active space and basis set size, but the error will remain fairly consistent.