M. Scott Shell¹, Pablo G. Debenedetti¹ and Frank H. Stillinger²

¹ Department of Chemical Engineering, Princeton University, Princeton, NJ 08544, USA
² Department of Chemistry, Princeton University, Princeton, NJ 08544, USA

E-mail: shell@princeton.edu, pdebene@princeton.edu and fhs@princeton.edu
Received 23 June 2005, in final form 28 July 2005

Published 25 November 2005
Online at stacks.iop.org/JPhysCM/17/S4035

J. Phys.: Condens. Matter 17 (2005) S4035–S4046

Abstract

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 vo at time t = 0 and eventual displacement Dx at time t = Dt. 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.