Exploring Avenues beyond Revised DSD Functionals: II. Random-Phase Approximation and Scaled MP3 Corrections

For revDSD double hybrids, the Gorling-Levy second-order perturbation theory component is an Achilles' heel when applied to systems with significant near-degeneracy (static) correlation. We have explored its replacement by the direct random phase approximation (dRPA), inspired by the SCS-dRPA75 functional of Kallay and co-workers. The addition to the final energy of both a D4 empirical dispersion correction and of a semilocal correlation component lead to significant improvements, with DSD-PBEdRPA(75)-D4 approaching the performance of revDSD-PBEP86-D4 and the Berkeley omega B97M(2). This form appears to be fairly insensitive to the choice of the semilocal functional but does exhibit stronger basis set sensitivity than the PT2-based double hybrids (due to much larger prefactors for the nonlocal correlation). As an alternative, we explored adding an MP3-like correction term (in a medium-sized basis set) to a range-separated omega DSD-PBEP86-D4 double hybrid and found it to have significantly lower WTMAD2 (weighted mean absolute deviation) for the large and chemically diverse GMTKN55 benchmark suite; the added computational cost can be mitigated through density fitting techniques.

Automated summary

The study attempted to replace the Gorling-Levy second-order perturbation theory with the direct random phase approximation in handling systems with significant near-degeneracy correlation. The addition of a D4 empirical dispersion correction and a semilocal correlation component to the final energy of the double hybrid model led to significant improvements. Another alternative explored was the addition of an MP3-like correction term to a range-separated omega DSD-PBEP86-D4 double hybrid, resulting in significantly lower WTMAD2 for the GMTKN55 benchmark suite.