Fluctuation-dissipation ratio in an aging Lennard-Jones glass

By using extensive molecular dynamics simulations, we have determined the violation of the fluctuation-dissipation theorem in a Lennard-Jones liquid quenched to low temperatures. For this we have calculated X(C), the ratio between a one-particle time-correlation function C and the associated response function. Our results are best fitted by assuming that X(C) is a discontinuous, piecewise constant function. This is similar to what is found in spin systems with one-step replica symmetry breaking. This strengthens the conjecture of a similarity between the phase space structure of structural glasses and such spin systems.