On the stability of vacancy and vacancy clusters in amorphous solids

We find vacancies and vacancy clusters in an amorphous solid, comprised of 500 atoms and characterized by a Lennard–Jones potential, to be unstable both under static and dynamic (molecular dynamics) relaxation. The annealing-out of the vacant volume and the associated translational rearrangement of atoms occur at temperatures and times much smaller than for diffusion in a corresponding face–centred–cubic crystal. Vacancy clusters in a random–network mode! characterized by a Keating potential are observed to persist after static relaxation. These clusters and the network collapse to a more dense–packed structure when the bond–bending forces are set equal to zero and more than nearest–neighbour central–force interactions are included.