Dynamics of thermal vibrational motions and stringlike jump motions in three-dimensional glass-forming liquids.

Using molecular dynamics simulation on a glass-forming liquid in three dimensions, we investigate the thermal vibrational motions, the configuration changes caused by stringlike jump motions, and their close correlations. The heterogeneous vibrational motions are visualized in terms of a vibration length Si(t) defined for each particle i. The structure factor for the inhomogeneity of Si(t)(2) is also calculated, which exhibits considerable long wavelength enhancement. By examining the birth times of strings, they are shown to appear collectively and intermittently. We show that particles with larger Si(t) tend to trigger jump motions more frequently at later times than those with smaller Si(t). We also show that the particles with fewer bonds tend to have larger Si(t) and participate more frequently in the stringlike motions.