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–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.