Figures show the energy components (excluding dispersion) for the IL16 data set. The electrostatics term (Fig. ) is especially flat, with variations of no more than 1 kcal/mol across a wide range of Karlsruhe and Dunning basis sets. Excluding the double-ζ basis sets, because we know that E elst is not yet converged in double-ζ basis sets even for the S66 dimers, the variations in E elst are 0.1 kcal/mol. Exchange energies (Fig. ) also vary by only ∼ 1 kcal/mol if double-ζ basis sets are excluded from the comparison. In contrast, induction energies (Fig. ) span a range of ∼ 4 kcal/mol in the various triple-and quadruple-ζ basis sets. This analysis points to induction as the energy component wherein the overall errors in the interaction energies reside, which is consistent with the need for a δMP2 correction to achieve sub-kcal/mol accuracy.