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

TL;DR

Adding a third-order perturbation term to the XYG7 double hybrid functional significantly improves its accuracy on the GMTKN55 benchmark, rivaling more expensive methods and reducing the need for empirical dispersion corrections.

Contribution

The paper introduces a modified XYG7 functional with a KS-MP3 term that achieves state-of-the-art accuracy without relying on empirical dispersion corrections.

Findings

WTMAD2 reduced to 1.17 kcal/mol on GMTKN55

Dispersion correction becomes redundant with the new functional

A simplified 6-parameter functional achieves competitive accuracy without dispersion or post-LDA components

Abstract

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.