Fluctuation-dissipation relations and energy landscape in an out-of-equilibrium strong glass-forming liquid

We study the out-of-equilibrium dynamics following a temperature-jump in a model for a strong liquid, BKS-silica, and compare it with the well known case of fragile liquids. We calculate the fluctuation-dissipation relation, from which it is possible to estimate an effective temperature $T_{eff}$ associated to the slow out-of-equilibrium structural degrees of freedom. We find the striking and unexplained result that, differently from the fragile liquid cases, $T_{eff}$ is smaller than the bath temperature.