Thermodynamic signature of the onset of caged dynamics in glass-forming liquids

We examine the thermodynamics of supercooled liquids focusing on the immediate vicinity of an onset temperature, $TA,$ where system dynamics just begin to experience caging effects. Simulation data from a polymer model and from small molecule mixtures show, in agreement with experiment, that the configurational entropy becomes strongly temperature dependent below $TA.$ Since the diffusion coefficient follows the Adam-Gibbs relationship, our results clearly establish a thermodynamic connection to the localized dynamics of glass-forming liquids.