Aging in a simple glass former

Using molecular dynamics computer simulations we investigate the out-of-equ ilibrium dynamics of a Lennard-Jones system after a quench from a high temp erature to one below the glass transition temperature. By studying the radi al distribution function we obtain evidence that during the aging the syste m is very close to the critical surface of mode-coupling theory. Furthermor e, 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 diff erent from the one in equilibrium. By investigating the temperature and tim e 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.