Dynamic heterogeneity and non-Gaussian behaviour in a model supercooled liquid

We use a recently derived reformulation of the diffusion constant (Stillinger and Debenedetti 2005 J. Phys. Chem. B 109 6604) to investigate heterogeneous dynamics and non-Gaussian diffusion in a binary Lennard-Jones mixture. Our work focuses on the joint probability distribution of particles with velocity v0 at time t = 0 and eventual displacement x at time t = t . We show that this distribution attains a distinctive shape at the time of maximum non-Gaussian behaviour in the supercooled liquid. By performing a two-Gaussian fit of the displacement data, we obtain, in a non-arbitrary manner, two diffusive length scales inherent to the supercooled liquid and use them to identify spatially separated regions of mobile and immobile particles. (Some figures in this article are in colour only in the electronic version)