Melting points of alkali chlorides evaluated for a polarizable and non-polarizable model.

Accurate molecular models of pure alkali halides are a prerequisite for developing transferable models of molten salts that can predict the properties of complex salt mixtures, such as those including dissolved actinide species and metal ions. Predicting the melting point of a substance represents a rigorous test of model quality. To this end, we compute the melting points of the alkali chlorides for a popular non-polarizable and polarizable model. Neither model yields more accurate predictions of the melting points across the entire family of alkali chlorides. Further calculations suggest that this may be because neither model simultaneously represents both the solid and liquid phases with sufficient accuracy across all four alkali chlorides. We find that the deviation from experiment in the model enthalpy of melting may be a good indicator of the deviation from experiment in the model melting temperature. Since the enthalpy of melting is easier to calculate in simulation than melting temperature, it may be a useful quantity to target when developing new force fields for molten salts.