These data also clearly demonstrate the importance of including diffuse functions when calculating interaction energies. This can be seen most clearly from the double-ζ data but is true in triple-and quadruple-ζ basis sets as well, although the magnitude of the effect diminishes with the cardinality of the basis set. For the double-ζ basis sets, errors increase in a consistent way as the diffuse orbitals are trimmed, going from def2-SVPD (with a full complement of diffuse functions) to the "heavy-augmented" def2-ha-SVP basis set, to the "minimally-augmented" def2-ma-SVP basis, and finally to def2-SVP that contains no diffuse functions at all. The importance of diffuse basis functions is most significant in the hydrogen-bonded subset, where induction effects are important and where the aforementioned truncations of def2-SVPD increase the MAE from 1.2 kcal/mol (def2-SVPD) to 3.7 kcal/mol (def2-SVP), with an increase in the maximum error from 3.8 kcal/mol (def2-SVPD) to 8.6 kcal/mol (def2-SVP). Removal of the diffuse functions has a much smaller effect in systems that are dominated by dispersion.