The effect of basis set superposition error on the convergence of interaction energies

For the intermolecular interaction energies of ion-water clusters [OH-(H2O)(n) (n = 1,2), F-(H2O), Cl-(H2O), H3O+ (H2O)(n) (n = 1,2), and NH4+(H2O)(n) (n = 1,2)] calculated with correlation-consistent basis sets at MP2, MP4, QCISD(T), and CCSD(T) levels, the basis set superposition error is nearly zero in the complete basis set (CBS) limit. That is, the counterpoise-uncorrected intermolecular interaction energies are nearly equal to the counterpoise-corrected intermolecular interaction energies in the CBS limit. When the basis set is smaller, the counterpoise-uncorrected intermolecular interaction energies are more reliable than the counterpoise-corrected intermolecular interaction energies. The counterpoise-uncorrected intermolecular interaction energies evaluated using the MP2/aug-cc-pVDZ level is reliable.