A molecular dynamics study of the melting of alkali halide crystals

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Abstract
Computer simulations of the melting of alkali halides have been carried out using the method of molecular dynamics with force evaluation by the particle-particle/particle-mesh (P3M) technique. The simulated systems were cubic microcrystals of 512 ions, and all the features characterising physical melting were observed in these small systems. Melting was initiated at the surface of the crystal. The ionic pair potential had a simple power-law repulsion and the parameters of the simulation, namely the mass and radius ratios of the ions and the power of the repulsion, were varied in a series of simulations. The melting temperature, expressed in terms of the cohesive energy of the crystal, showed a systematic dependence on the radius ratio and it also varied with the hardness of the repulsion. Comparison with experiment suggests that a simple potential with a fixed value of the power of the repulsion is not able to reproduce the experimental melting temperatures and latent heats. The hardness of the repulsion has an important effect on melting temperatures.