A major motivation of this work was to generate data for benchmarking and improving MC-PDFT. As a first use of our data to optimize MC-PDFT functionals, we have investigated the optimal mixing parameter λ for hybrid tPBE (htPBE, for which the energy is given by λE SA-CASSCF + (1 -λ)E tPBE ) over the Aug (12,12) database. We have chosen this set of excitations because it is likely to have the smallest amount of poor active spaces erroneously included by the T SA-CASSCF = 1.1 eV error threshold. In other words, we expect this set of excitations to have the largest percentage of well-chosen active spaces. Figure shows the optimization of λ on the Aug(12,12) set of included excitations. Delightfully, we find that λ = 0.25 -the same parameter used in tPBE0 -is optimal for this set of excitations, in agreement with the much smaller study previously conducted on the EE27 database. Therefore we recommend using tPBE0 for excitation energies in the general case and especially for excitations similar to those in the QUESTDB dataset. Optimizing the parameter over all active spaces and basis sets results in only a slightly shifted value of λ = 0.3, which appears to be offset mostly by the greater number of poor active spaces included in the Jun(8,8) excitation energies (SI Figure ); using the more robust tPBE0 error threshold (discussed in the SI) removes this discrepancy (SI Figure ). This suggests that a higher value of λ may be optimal for cases in which wave function error dominates.