The chlorate (ClO - 3 ) ion represents the lone exception to an otherwise systematic correlation between classical and quantum-chemical interaction energies. This particular species is much more strongly solvated by AMOEBA ( E int = -126.6 ± 9.9 kcal/mol in bulk water) than it is by SAPT0 + MBD ( E int = -85.8 ± 10.0 kcal/mol). Considering the chlorine oxyanions as a group, the trend amongst the AMOEBA values of