An evaluation of local double hybrid density functionals

Abstract

First steps towards range-separated local double hybrid (RSLDH) functionals are reported. Optimizations using human-designed local mixing functions (LMFs) for the position-dependence of exact exchange led either to a vanishing perturbational correlation contribution or to a constant LMF, i.e., to the $\omega$DH25 double hybrid. $\omega$DH25-D4 achieves the so far lowest WTMAD-2 value (2.13 kcal/mol) of a gDH for the GMTKN55 test suite. Then an “n-LMF” was optimized as a shallow neural network, giving the first true RSLDHs, so far in a post-$\omega$DH25 manner. A well-structured LMF and WTMAD-2 values down to 1.88 kcal/mol are obtained, without calibrating exchange-energy densities.