Aging in a simple glass former

Using molecular dynamics computer simulations we investigate the out-of-equilibrium dynamics of a Lennard-Jones system after a quench from a high temperature to one below the glass transition temperature. By studying the radial distribution function we obtain evidence that during the aging the system is very close to the critical surface of mode-coupling theory. Furthermore, we show that two-time correlation functions show a strong dependence on the waiting time elapsed since the quench and that their shape is very different from the one in equilibrium. By investigating the temperature and time dependence of the frequency distribution of the normal modes we show that the energy of the inherent structures can be used to define an effective (time-dependent) temperature of the aging system.