Crossover from Equilibration to Aging: (Non-equilibrium) Theory vs. Simulations

Understanding glasses and the glass transition requires comprehending the nature of the crossover from the ergodic (or equilibrium) regime, in which the stationary properties of the system have no history dependence, to the mysterious glass transition region, where the measured properties are non-stationary and depend on the protocol of preparation. In this work we use non-equilibrium molecular dynamics simulations to test the main features of the crossover predicted by the \emph{molecular} version of the recently-developed multicomponent non-equilibrium self-consistent generalized Langevin equation (NE-SCGLE) theory. According to this theory, the glass transition involves the abrupt passage from the ordinary pattern of full equilibration to the aging scenario characteristic of glass-forming liquids. The same theory explains that this abrupt transition will always be observed as a blurred crossover by the unavoidable finiteness of the time window of any experimental observation. We find that within their finite waiting-time window, the simulations confirm the general trends predicted by the theory.