Collective jumps in a soft-sphere glass

Relaxations in a soft-sphere glass are studied by molecular dynamics. We observe local-jumps where groups of ten and more atoms move collectively forming chainlike structures. At the lowest temperatures the total jump length is of the order of the nearest neighbor distance whereas a single atom moves only a fraction of this distance. Both the displacements and the numbers of pa;participating atoms increase with temperature. Successive jumps tend to involve the same atoms. Relaxations and soft quasilocalized vibrations are correlated. In the glass and in the liquid state near the glass transition a markedly non-Gaussian distribution of the mean square displacements is observed. [S0163-1829(99)10601-5].