Dispersion-corrected r²SCAN based double-hybrid functionals

The regularized and restored semi-local meta-generalized gradient approximation (meta-GGA) exchange-correlation functional r²SCAN [J. W. Furness, A. D. Kaplan, J. Ning, J. P. Perdew, and J. Sun, J. Phys. Chem. Lett. 11, 8208–8215 (2020)] is used to create adiabatic-connection-derived global double-hybrid functionals employing spin-opposite-scaled MP2. The 0-DH, CIDH, QIDH, and 0-2 type double-hybrid functionals are assessed as a starting point for further modification. Variants with 50% and 69% Hartree--Fock exchange (HFX) are empirically optimized (Pr²SCAN50 and Pr²SCAN69), and the effect of MP2-regularization (κPr²SCAN50) and range-separated HFX (ωPr²SCAN50) is evaluated. All optimized functionals are combined with the state-of-the-art London dispersion corrections D4 and NL. The resulting functionals are assessed comprehensively for their performance on main-group and metal-organic thermochemistry on 90 different benchmark sets containing 25800 data points. These include the extensive GMTKN55 database, additional sets for main-group chemistry, and multiple sets for transition-metal complexes including the ROST61, the MOR41, and the MOBH35 sets. As the main target of this study is the development of a broadly applicable, robust functional with low empiricism, special focus is put on variants with moderate amounts of HFX (50%) which are compared to the so far successful PWPB95-D4 (50% HFX, 20% MP2 correlation) functional. The overall best variant, ωPr²SCAN50-D4, performs well on main-group and metal-organic thermochemistry, followed by the Pr²SCAN69-D4 that offers a slight edge for metal-organic thermochemistry, and by the low HFX global double-hybrid Pr²SCAN50-D4 that performs robustly across all tested sets. All four optimized functionals, Pr²SCAN69-D4, Pr²SCAN50-D4, κPr²SCAN50-D4, and ωPr²SCAN50-D4 outperform the PWPB95-D4 functional.