Knowledge of the dynamics in amorphous silicon that occurs through a sequen
ce of discrete activated events is essential to predict many of the associa
ted physical and chemical properties. Using the recently introduced nudged
elastic band method of Jonsson, Mills, and Jacobsen and a modified empirica
l Stillinger-Weber potential, we investigate, in detail, 802 perfect events
generated with the activation-relaxation technique. We find that a large n
umber 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-excha
nge mechanism of Wooten, Winer, and Weaire is, by far, the most important o
ne for nondefect based dynamics in a-Si.