Glass Transition

Computer simulations of melting, crystallization, glass transition, and annealing for a model system of 864 Lennard-Jones (LJ) atoms under a periodic boundary condition are carried out using constant-pressure molec ular dynamics techniques with temperature control. When an fcc crystal of LJ atoms is heated, melting occurs; however, an LJ liquid, when quenched slowly, crystallizes into layers with stacking faults. Each layer forms a two-dimensional, close-packed structure with occasional point defects but without dislocations. When the quench rate is high enough, an LJ liquid transforms into a disordered structure without a discontinuous change in volume. The dependence of the glass transi tion on the quench rate is determined by examining macroscopically observable physical features. Several microscopic structure parameters are introduced to ana lyze, at the atomic level, the structures of glasses pro duced by different quench rates. When annealed, a glass made with a low enough quench rate is stable against crystallization. Identifying the number of atoms in the system having local icosahedral symmetry is a prom ising method of characterizing the glass's stability. The microscopic structural changes in the annealing pro cesses are presented in the companion video to this paper.