Do Double Hybrid Functionals Benefit from Regularization in the PT2 term? Observations from an Extensive Benchmark

We put to the test a recent suggestion [Shee, J.; Loipersberger, M.; Rettig, A.; Lee, J.; Head-Gordon, M. J. Phys. Chem. Lett. 2021, 12 (50), 12084–12097] that MP2 regularization might improve the performance of double-hybrid density functionals. Using the very large and chemically diverse GMTKN55 benchmark, we find that κ-regularization is indeed beneficial at lower percentages of Hartree-Fock exchange, especially if spin-component scaling is not applied (such as in B2GP-PLYP or ωB97M(2)). This benefit dwindles for DSD and DOD functionals, and vanishes entirely in the ca. 70% HF exchange region optimal for them.