Melting of atomic solids: effect of range and softness of interaction potentials

The relationship between the behaviour at melting and the range and softness of interatomic potentials is explored using Monte Carlo simulations of bulk Morse and Lennard-Jones systems. The range parameter of the Morse interaction is tuned to mimic the variation seen in atomic systems, from metallic systems with soft, long-range interactions to van der Waals solids with short-range, strongly repulsive potentials. An umbrella sampling procedure is used to determine the melting point by constructing Landau free energy curves; the accuracy and finite-size effects associated with this approach are estimated for the Lennard-Jones system by comparison with existing results in the literature. The melting temperature as well as the strength of the first-order transition for Morse solids is shown to increase as the range and softness of the interatomic interactions decrease. The phase transition properties are largely determined by the behaviour of the pair interaction near equilibrium separation. The height of the barrier separating the two phases, as determined from the Landau free energy curve, is shown to be correlated with the crystal-liquid interfacial free energy.