N-POL MD simulations with box #4 at both conditions show almost no La-Cl dissociation resulting in CN > 2. The presence of high-energy barriers for dissociation (∼7 k B T, Table ) at both conditions is the reason why La-Cl dissociation is kinetically unfavorable in N-POL MD. Similar conclusions were drawn by Zhang and Yan with a different set of pair potentials at similar temperature conditions. As the existing N-POL potentials were optimized to reproduce structures at ambient conditions, we attempted to refit the LJ potential from Migliorati et al. with atomic force data at supercritical conditions. However, this refitted potential also predicted unfavourable La-Cl dissociation. The observed inability of LJ-type potentials to predict the hydration free energies and ion-oxygen distances of divalent cations was already addressed by Li et al. , who attributed this behavior to the lack of ion-dipole interactions. These problems are overcome with PIM, which softens the La-Cl interactions resulting in significant dissociation at both conditions, consistent with AIMD simulations and extended X-ray absorption fine structure (EXAFS) data at similar conditions.