In contrast to the AMOEBA results, the SAPT0 + MBD calculations afford similar ensemble-averaged interaction energies for both ClO - 3 and ClO - 4 , meaning that the ClO - 3 value seems anomalously small, given that all of the chlorine oxyanions except for ClO - 4 has a sizable dipole moment. As a sanity check, we recomputed interaction energies for all of the ions using SAPT0(KS) + MBD, which includes intramolecular electron correlation. These results are plotted in Fig. (a), which should be compared to the corresponding SAPT0 + MBD results in Fig. (a). Total interaction energies at either level of theory are quite comparable, and in particular both methods exhibit the same trend amongst the ClO - n ions, which differs from the trend predicted by AMOEBA.