Surprisingly Good Performance of XYG3 Family Functionals Using a Scaled KS-MP3 Correlation

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