TRANSLATIONAL DIFFUSION ON HETEROGENEOUS LATTICES - A MODEL FOR DYNAMICS IN GLASS-FORMING MATERIALS

Simulations of translational motion on lattices with spatially heterog eneous dynamics have been performed, Translation occurs by nearest nei ghbor jumps on a three-dimensional simple cubic lattice. The overall l attice is subdivided into cubic blocks. The rate for jumps within a gi ven block is controlled by the local relaxation time (or rotation time ) for that block. Blocks exchange their local relaxation times on a sp ecified time scale. If the local distribution of relaxation times is g iven by a Kohlrausch-Williams-Watts distribution, the simulation resul ts can reproduce experimental observations of enhanced translational d iffusion in supercooled liquids. This adds further weight to arguments that dynamics in deeply supercooled liquids are spatially heterogeneo us and that this heterogeneity is responsible for the non-exponential relaxation functions which are often observed. For systems with only t wo local relaxation times, the simulation results are in good agreemen t with effective medium theory.