Glass Transition and Stability of Glasses: Simulations and Visual Presentations by Computer Graphics

Abstract

Computer simulations of crystallization, glass transition, and annealing for a model system composed of 864 Lennard-Jones (LJ) atoms under a periodic boundary condition, are carried out using constant-pressure molecular dynamics techniques with temperature control. An LJ liquid, when quenched slowly, crystallizes into a stack of layers with stacking faults. Each layer forms a two-dimensional close-packed structure with occasional point defects but without any 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 transition on the quench rate is determined by examining macroscopidally observable physical features such as thermodynamic, structural, and dynamic properties. Several microscopic structure parameters are introduced in order to analyze, at the atomic level, the structures of the glasses produced by different quench rates. When annealed, a glass carefully made with a low enough quench rate is stable against crystallization. The number of atoms in the system having local icosahedral symmetry is identified as a promising measure of characterizing the stability of a glass.