Spatial correlations of mobility and immobility in a glass-forming Lennard-Jones liquid

Using extensive molecular dynamics simulations of an equilibrium, glass-for ming Lennard-Jones mixture, we characterize in detail the local atomic moti ons. We show that spatial correlations exist among particles undergoing ext remely large ("mobile") or extremely small:("immobile") displacements over a suitably chosen time interval. The immobile particles form the cores of r elatively compact clusters, while the mobile particles move cooperatively a nd form quasi-one-dimensional stringlike clusters. The strength and length scale of the correlations between mobile particles are found to grow strong ly with decreasing temperature, and the mean cluster size appears to diverg e near the mode-coupling critical; temperature. We show that these correlat ions in the particle displacements are related to equilibrium fluctuations in the local potential energy and local composition. [S1063-651X(99)06309-6 ].