Accurate Intermolecular Interaction Energies Using Explicitly Correlated Local Coupled Cluster Methods [PNO-LCCSD(T)-F12].

We present benchmark results for the A24, S66, and X40 sets of intermolecular interaction energies obtained with our recently developed PNO-LCCSD(T)-F12 method. Using the aug-cc-pVQZ-F12 basis set and tight domain options, the root-mean-square (RMSD) and maximum (MAXD) deviations from the currently best CCSD(T)/CBS estimates for the S66 set amount to only 0.02 and 0.06 kcal mol, respectively. The corresponding triple-ζ (aug-cc-pVTZ-F12) results are similarly accurate, and even with double-ζ (aug-cc-pVDZ-F12) basis sets the RMSD and MAXD deviations amount to only 0.05 and 0.11 kcal mol, respectively. Preliminary PNO-LCCSD(T)-F12 calculations on the X40 set of intermolecular interactions of halogenated molecules yield interaction energies in reasonable agreement with the original CCSD(T)/CBS estimates. The PNO-LCCSD(T)-F12 method does not rely on error cancellations as the popular ΔCCSD(T) approach and can yield comparable or better accuracy at a fraction of the cost. This accuracy is of importance for studying reactions involving large molecules, in which intramolecular noncovalent interactions are important and no counterpoise corrections are possible.