Assessment of the DLPNO Binding Energies of Strongly Noncovalent Bonded Atmospheric Molecular Clusters

This
work assesses the performance of DLPNO-CCSD­(T0),
DLPNO-MP2, and density functional theory methods in calculating the
binding energies of a representative test set of 45 atmospheric acid–acid,
acid–base, and acid–water dimer clusters. The performance
of the approximate methods is compared to high level explicitly correlated
CCSD­(F12*)­(T)/complete basis set (CBS) reference calculations. Out
of the tested density functionals, ωB97X-D3­(BJ) shows the best
performance with a mean deviation of 0.09 kcal/mol and a maximum deviation
of 0.83 kcal/mol. The RI-CC2/aug-cc-pV­(T+d)­Z level of theory severely
overpredicts the cluster binding energies with a mean deviation of
−1.31 kcal/mol and a maximum deviation up to −3.00 kcal/mol.
Hence, RI-CC2/aug-cc-pV­(T+d)­Z should not be utilized for studying
atmospheric molecular clusters. The DLPNO variants are tested both
with and without the inclusion of explicit correlation (F12) in the
wavefunction, with different pair natural orbital (PNO) settings (loosePNO,
normalPNO, and tightPNO) and using both double and triple zeta basis
sets. The performance of the DLPNO-MP2 methods is found to be independent
of PNO settings and yield low mean deviations of −0.84 kcal/mol
or below. However, DLPNO-MP2 requires explicitly correlated wavefunctions
to yield maximum deviations below 1.40 kcal/mol. For obtaining high
accuracy, with maximum deviation below ∼1.0 kcal/mol, either
DLPNO-CCSD­(T0)/aug-cc-pVTZ (normalPNO) calculations or
DLPNO-CCSD­(T0)-F12/cc-pVTZ-F12 (normalPNO) calculations
are required. The most accurate level of theory is found to be DLPNO-CCSD­(T0)-F12/cc-pVTZ-F12 using a tightPNO criterion which yields
a mean deviation of 0.10 kcal/mol, with a maximum deviation of 0.20
kcal/mol, compared to the CCSD­(F12*)­(T)/CBS reference.