Solid-liquid phase transitions in Lennard-Jones systems

A modified cell model is used for the solid-liquid phase transition in the low-pressure region for Lennard-Jones systems. Effects due to randomness of neighboring atomic positions are included in the cell potential. The free energy is then calculated after imposing self-consistent conditions on cell irregularity. Two minima are observed on the free energy versus cell dimension curves, leading to bifurcations into solid and liquid phases by double-tangent construction. The theoretical results in the low-pressure region are in good agreement with molecular dynamics results and also with the experimental data or argon.