In contrast to IL16, overall errors in the interaction energies for the AHB21 and CHB6 data sets follow more discernible and systematic trends; see Table . The smallest MAEs (1.2-1.5 kcal/mol) are obtained using the aug-cc-pVQZ and def2-QZVPD basis sets. Trimming the diffuse functions at the triple-ζ level has a noticeably detrimental effect on the anion-neutral dimers in the AHB21 data set. This effect, which was not seen in dimers of neutral molecules, is less evident at the quadruple-ζ level. In general the basis-set demands for these ion-containing dimers are more severe than they are for the S22 and S66 dimers. 4.5. Halide-Water Clusters. For the S66 data set we found that induction energies exhibit remarkably little basis set dependence (see Fig. ), which might simply reflect that the induction energies for these small, chargeneutral dimers are not especially large. That the ionic test systems considered in Section 4 .4 exhibit somewhat more stringent basis-set requirements comports with this hypothesis. To test this further, we next consider some larger anion-water clusters whose induction energies are more significant. 4.5.1. Aqueous Chloride Ion. We first consider Cl -(H 2 O) n clusters extracted from a molecular dynamics simulation of Cl -(aq), and which have previously been used to explore the energetics of ion hydration. A set of 51 clusters containing an average of n = 28 water molecules (representing two solvation shells) was taken from previous work, and we will examine basis-set effects on the energy components across this trajectory. These calculations are meant to investigate what (if any) cancellation one can expect across a set of similar geometries for the same system and for the purposes of these calculations each Cl -(H 2 O) n snapshot is treated as a dimer, with Cl -as one monomer and (H 2 O) n as the other. As a representative example of a high-throughput application, we examine some very efficient basis sets such as 6-31+G(d) and 6-311+G(d,p) in addition to higher-quality ones such as def2-TZVPD and some intermediate choices as well. Calculations were performed at the XSAPT + ai D3 level and δE HF is not included in the induction energy for these calculations, in the interest of computational expedience. We expect the convergence behavior of the second-order induction terms in eq. 2 to be similar to that of δE HF . The first half of the data set is sufficient to exhibit both the minimum and maximum value of each energy component so for clarity only those data are shown, in Fig. .