Aging effects manifested in the potential-energy landscape of a model glass former

We present molecular dynamics simulations of the binary Kob-Andersen Lennard-Jones model, a model glass former, and consider the distributions of inherent energies and metabasins during aging. In addition to the typical protocol of performing a temperature jump from a high temperature to a low destination temperature, we consider the temporal evolution of the energy distributions after an "up-jump," i.e., from a low to a high temperature. In this case, for times on the order of the relaxation time the distribution of metabasin energies exhibits a transient two-peak structure for a small system (65 particles). For a large system (1000 particles) no such two-peak structure appears because it is averaged out. The simulations show, however, that a clear signal of an intermediate two-peak structure survives in the thermodynamic limit, namely that the inherent energy distribution width goes through a maximum at intermediate times for temperature up jumps; no such maximum is found for temperature down jumps. These findings are qualitatively rationalized in terms of a simple trap model with a Gaussian distribution of energies, assuming that the liquid may be divided into non-interacting regions each of which is described by a trap model.