The two‐dimensional Lennard‐Jones system: Sublimation, vaporization, and melting

The solid–vapor equilibrium line and the liquid–vapor equilibrium line near the melting region for classical two‐dimensional systems of particles interacting by Lennard‐Jones (12,6) pair potentials are determined from Monte Carlo simulations with 224 particles. Structural and thermodynamic properties are evaluated for homogeneous single phases on both sides of the melting transition. The Monte Carlo results show that a cell model approximation to the solid phase has good accuracy for most of the anharmonic 2D solid conditions of this work. Free energies for solid states are constructed starting from the low temperature quasiharmonic solid; for the 2D liquid states the starting point is the virial expansion for the dilute gas. From these free energies the triple‐point melting of the periodically extended 224‐particle system is found to be first order and the latent heat of melting is determined. Graphic displays are obtained showing the occurrence of dislocation pairs, voids, particle exchange, and mixed p...