Interaction energies defined in Eq. (1) do not include relaxation of the monomer geometries, so E int is an interaction energy in the "vertical" sense, not a binding energy or a solvation energy. In considering the ion-water clusters X -(H 2 O) n extracted from MD simulations, we treat the entire water cluster (H 2 O) n as a single monomer for the purpose of computing E int and its components, then average over the ensemble of snapshots. Even so, the value E int corresponds to vertical removal of the ion. It includes the change in (electronic) polarization of the water molecules upon removal of the ion but does not include the (orientational) reorganization energy of the water to fill the void left behind by the ion.