Isothermal–isobaric computer simulations of melting and crystallization of a Lennard-Jones system

By means of constant-temperature, constant-pressure molecular dynamics techniques, we simulate the melting and crystallization processes of a model system composed of 864 Lennard-Jones (LJ) particles under periodic boundary conditions. On heating an fcc crystal of LJ particles, it is ascertained that melting takes place. On the other hand, a LJ liquid, when quenched slowly, crystallizes into a stacking of layers with stacking faults where each layer forms a close-packed structure with occasional point defects. The atomic configuration is not always nucleated into a completely ordered structure. A large hysteresis in the volume-temperature curve is observed. The volume contraction at the transition is characterized by two different growth rates, relatively slow at the first stage and relatively fast at the final stage. The critical cooling rate which separates the crystal-forming cooling rates and the glass-forming cooling rates is between 4×1010 and 4×1011 K/s for argon. On taking advantage of computer simulations, we analyze the microscopic atomic structure of our LJ system on the basis of the Voronoi and Delaunay tessellation.