How distributed charge reduces the melting points of model ionic salts

Using coarse grain model ions and NPT molecular dynamics simulations, we determine melting point trends across a set of salts beginning with a system closely akin to the restricted primitive model. Redistributing the cation charge in salts with size-symmetric, monovalent, spherical ions can reduce the melting temperature by up to 50% compared to the charge-centered case. Displacing the charge from the ion center reduces the enthalpy of the liquid more than that of the solid resulting in a lower melting point. Upon cooling from the liquid phase, the model salts considered either crystallize as orientationally-disordered CsCl solids, or become trapped in glassy states, depending on the amount and extent of the cation charge redistribution. For the latter case, we find an orientationally-ordered crystal structure with space group 111 (P_{bar{4}2m}) underlying the glassy states. The structural and dynamical properties of both the solid and liquid phases of the model salts are discussed in some detail.