Central role of thermal collective strain in the relaxation of structure in a supercooled liquid

The spatial distribution of structural relaxation in a supercooled liquid is studied using molecular dynamics simulations of a two-dimensional binary mixture. It is shown that the spatial heterogeneity of the relaxation along with the time scale of the relaxation is determined, not by the frequency with which particles move a distance pi/2k(Bragg), but by the frequency with which particles can achieve persistent displacements. We show that these persistent displacements are achieved through the coupled action of local reorganizations and unrecoverable thermal strains.