Exploring CPS-extrapolated DLPNO-CCSD(T1) reference values for benchmarking DFT on enzymatically catalyzed reactions

Domain-based local pair natural orbital Coupled Cluster Singles Doubles with Perturbative Triples [DLPNO-CCSD(T)] is regularly used to calculate reliable benchmark reference values at a significantly lower computational cost compared to canonical CCSD(T). Recent work has shown that even greater accuracy can be obtained at only a small additional cost through extrapolation to the complete PNO space (CPS) limit. Herein we test two levels of CPS extrapolation—CPS(5,6), which approximates the accuracy of standard TightPNO, and CPS(6,7), which surpasses it—as benchmark values to test density functional approximations (DFAs) on a small set of organic and transition-metal enzyme active site models. Between the different reference levels of theory there are changes in the magnitudes of the absolute deviations for all functionals, and the relative ranking of the methods is also affected. We thus update the reference values for our entire ENZYMES22 benchmark set to the DLPNO-CCSD(T)/CPS(6,7)/CBS level of theory. Against these new references, CAM-B3LYP-D3(BJ) stands out as the surprisingly most robust DFA for calculating barrier heights and reaction energies associated with the assessed organic enzymatically catalyzed reactions.