Molecular Dynamics Simulation of Vitrification and Plastic Deformation of a Two‐Dimensional Lennard‐Jones Mixture

A computer model of a two‐dimensional atomic glass is generated by molecular dynamics. This model consists of 500 Lennard‐Jones particles of two different diameters. A volume‐temperature diagram is obtained. The bend found on this diagram at T = 0.28 ϵ is interpreted as the glass transition. Density fluctuations and changes in the particles coordination numbers at the glass transition are studied by means of Voronoy polygons. The spatial correlation functions for particle displacements in the liquid and glassy states are analyzed. It is found that the glass structure is always a frozen liquid structure. Below the glass transition particle displacements from their equilibrium positions become spatially correlated, and the correlation length is greater than the model's size. Unusual roton‐like collective vibrational modes are found in the glass. The simulation of shear deformation shows that these modes may play an important role in the plastic deformation. No correlation is found between the diffusional mobility of particles and their local free volumes. This fact contradicts the main physical concept upon which a free volume approach is based.