Democratic particle motion for metabasin transitions in simple glass formers.

We use molecular dynamics computer simulations to investigate the local motion of the particles in a supercooled binary liquid. Using the concept of the distance matrix, we find that the alpha relaxation corresponds to a small number of crossings from one metabasin to a neighboring one. Each crossing is very rapid and involves the collective motion of O(40) particles that form a relatively compact cluster, whereas stringlike motions seem not to be relevant for these transitions. These compact clusters are thus potential candidates for the cooperatively rearranging regions proposed a long time ago by Adam and Gibbs.