  By adding a GLPT3 (third-order G\"orling-Levy perturbation theory, or KS-MP3)
term E3 to the XYG7 form for a double hybrid, we are able to bring down WTMAD2
(weighted total mean absolute deviation) for the very large and chemically
diverse GMTKN55 benchmark to an unprecedented 1.17 kcal/mol, competitive with
much costlier composite wavefunction ab initio approaches. Intriguingly: (a)
the introduction of E3 makes an empirical dispersion correction redundant; (b)
GGA or mGGA semilocal correlation functionals offer no advantage over LDA in
this framework; (c) if a dispersion correction is retained, then simple Slater
exchange leads to no significant loss in accuracy. It is possible to create a
6-parameter functional with WTMAD2=1.42 that has no post-LDA DFT components and
no dispersion correction in the final energy.
