A quantitative measure of the time scale at which Fickian diffusion began in supercooled liquids was proposed, and Brownian dynamics computer simulations were used to determine the temperature dependence of this onset time in a Lennard-Jones binary mixture. The time for the onset of Fickian diffusion ranged from 6.5 to 31 times the α relaxation time (where the α relaxation time was the characteristic relaxation time of the incoherent intermediate scattering function). The onset time increased faster with decreasing temperature than the α relaxation time. Mean-squared displacement at the onset time increased with decreasing temperature.

Timescale for the Onset of Fickian Diffusion in Supercooled Liquids. G.Szamel, E.Flenner: Physical Review E, 2006, 73[1], 011504 (4pp)