where α is the percentage of exact or HF exchange, E HF x . Our intention is not to carefully optimize α but rather to understand whether α = 50, representing the BH&H-LYP functional in eq. 2, is merely a point along a continuum or something worthy of special consideration. Because the functionals BHandH and BH&H-LYP are available by name in many quantum chemistry programs, we must consider the possibility that their recurring presence in the literature simply reflects available keywords. In the end, however, we find that 50% exact exchange does seem to have advantages compared to slightly larger or smaller values of α. Note that all functionals will be dispersion-corrected, which is necessary to obtain competitive thermochemical benchmarks in modern DFT. 104-109 2 Methods 2.1. Data Sets. The data sets used to benchmark ground-state properties (thermochemistry and barrier heights) are described in Section 2 .1 .1, while those used for vertical excitation energies are discussed in Section 2 .1 .2.