Accurate Intermolecular Interaction Energies Using Explicitly Correlated Local Coupled Cluster Methods...

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^-1, 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^-1, 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.