Dislocation mobility in two-dimensional Lennard-Jones material

In seeking to understand at a microscopic level the response of dislocation s to stress, we have undertaken to study as completely as possible the simp lest case: a single dislocation in a two-dimensional crystal. The intention is that results from this study will be used as input parameters in larger length scale simulations involving many defects. We present atomistic simu lations of defect motion in a two-dimensional material consisting of atoms interacting through a modified Lennard-Jones potential. We focus on the reg ime where the shear stress is smaller than its critical value, where there is a finite energy barrier for the dislocation to hop one lattice spacing. In this regime motion of the dislocation will occur as single hops through thermal activation over the barrier. Accurate knowledge of the barrier heig ht is crucial for obtaining rates of such processes. We have calculated the energy barrier as a function of two components of the stress tenser in a s mall system, and have obtained good fits to a functional form with only a f ew adjustable parameters. We examine prefactors, finite temperature and dyn amics. (C) 2001 Elsevier Science B.V. All rights reserved.