Dynamic heterogeneity and non-Gaussian behavior in a model supercooled   liquid
  We use a recently-derived reformulation of the diffusion constant [Stillinger F H and Debenedetti P G 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 v_0 at time t=0 and eventual displacement Delta x at time t=Delta t. We show that this distribution attains a distinctive shape at the time of maximum non-Gaussian behavior 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. 
M. Scott Shell, Pablo G. Debenedetti, Frank H. Stillinger