Molecular dynamical studies of the motion of point defects in a crystalline lattice

Abstract

The authors have applied molecular dynamical type of calculations to the study of the motion of interstitials and vacancies in a crystalline lattice. The purpose was to investigate the effects of lattice thermal oscillations on the motion and the interactions of these simple defects and to study the 'random walk' problem of defect motion on an atomic scale. The lattice model was a three dimensional body centred cubic (bcc) model with a central force interaction potential which extended to second neighbours and simulated the interaction energies in alpha -iron. The lattice containing one or more defects was first relaxed statically to a configuration of minimum energy, corresponding to the condition of zero absolute temperature. A temperature was then given to the lattice by assigning a Maxwellian distribution to the velocity components of the lattice points in a random order. The subsequent motion of the lattice points and of the defects was calculated according to classical mechanics. The dynamical results showed that the temperature dependence of the jump frequency of the defects was in general agreement with the random walk theory of atomic diffusion. From this temperature dependence, the energy and the entropy of defect migration were obtained.