Optimal activation and diffusion paths of perfect events in amorphous silicon

Knowledge of the dynamics in amorphous silicon that occurs through a sequence of discrete activated events is essential to predict many of the associated physical and chemical properties. Using the recently introduced nudged elastic band method of Jonsson, Mills, and Jacobsen and a modified empirical Stillinger-Weber potential, we investigate, in detail, 802 perfect events generated with the activation-relaxation technique. We find that a large number of the high-energy events contain, in fact, two or more "subevents." With this result included, the average barrier height goes down to about 3.0 eV, in line with experimental values and we also find that the bond-exchange mechanism of Wooten, Winer, and Weaire is, by far, the most important one for nondefect based dynamics in a-Si.