  For the large and chemically diverse GMTKN55 benchmark suite, we have studied
the performance of density-corrected density functional theory (HF-DFT),
compared to self-consistent DFT, for several pure and hybrid GGA and meta-GGA
exchange-correlation (XC) functionals (PBE, BLYP, TPSS, SCAN) as a function of
the percentage of HF exchange in the hybrid. The D4 empirical dispersion
correction has been added throughout. For subsets dominated by dynamical
correlation -- particularly noncovalent interaction subsets -- HF-DFT is highly
beneficial, particularly at low HF exchange percentages. For subsets with
significant static correlation (i.e., where a Hartree-Fock determinant is not a
good zero-order wavefunction), HF-DFT may do more harm than good. While the
self-consistent series show optima at or near 37.5% (i.e., 3/8) for all four XC
functionals -- consistent with Grimme's proposal of the PBE38 functional --
HF-BnLYP-D4, HF-PBEn-D4, and HF-TPSSn-D4 all exhibit minima nearer 25% (i.e.,
1/4). Intriguingly, for HF-SCANn-D4, the minimum is near 10%, but the weighted
mean absolute error (WTMAD2) for GMTKN55 is only barely lower than that of
HF-SCAN-D4 (i.e., where the post-HF step is a pure meta-GGA). The latter
becomes an attractive option, only slightly more costly than pure Hartree-Fock,
and devoid of adjustable parameters other than the three in the dispersion
correction. Moreover, its WTMAD2 is only surpassed by the highly empirical
M06-2X and by the combinatorically optimized empirical range-separated hybrids
wB97X-V and wB97M-V.
