Insights into the role of dynamic heterogeneity in reorientational and translational dynamic measurements from simulations in the isoconfigurational ensemble

A major question in the study of the glass transition over the last 50 years has been the origin of stretched exponential relaxation and its connection to the observations of non-Gaussian dynamics and decoupling phenomena such as Stokes-Einstein breakdown. The proposition that these phenomena all emerge from averaging over spatial dynamic heterogeneity has emerged as a major view of the common origin of these phenomena. However, significant questions remain, such as the frequent observation that stretching exponents obtained from dielectric spectroscopy commonly do not exhibit the pronounced temperature dependence expected to accompany growing dynamic heterogeneity on cooling. Here we employ molecular dynamic simulations of glass-forming dimers and bead-spring polymers in the isoconfigurational ensemble to quantify the extent to which each of these phenomena emerge from spatial averaging vs locally anomalous dynamics. Results point to important differences between the role of dynamic heterogeneity in reorientational and translational dynamic quantities such as those measured by dielectric spectroscopy and neutron scattering respectively.