Changes in temperature and latent h

Changes in temperature and latent heat of melting in a series of alkali halides were analyzed using molecular dynamics (MD) with pair potential, wherein only the Born-Mayer short-range repulsion and the long-range Coulomb interaction were taken into account. The trends of melting properties connected with this were considered via a hypothetical model where the ionic radii of an alkali halide are supposed to be continuous variables. The values of potential parameters for ion pairs presented in lithium, sodium and potassium halides were calculated by means of the second-order Møller-Plesset perturbation theory. Two MD techniques were compared: in the first case, the crystal was gradually heated to observe a density drop indicating melting. In the second, solid and liquid coexistence was simulated with pressure and enthalpy being fixed (NPH ensemble), with separate preparation paths of the phases being carried out at constant pressure and temperature. Better agreement with the experimental data was found when the simulation was performed via the solid-liquid coexistence in a single cell. A general explanation for the deviation of lithium halides’ melting properties from the general trend of a decrease in the melting temperature with an increase in the lattice parameter was proposed. It was illustrated how the mismatch in the cation and anion radii have an effect on the melting properties of alkali halides.