Computer Simulations of Non-Equilibrium Dynamics in Silica

We present results from molecular dynamics computer simulations of aging silica (modeled by the BKS model). The system is equilibrated at $T_{\rm i}=5000$~K and quenched instantaneously to $T_{\rm f}=2500$~K. After a waiting time $t_{\rm w}$ we investigate the dynamics of the Si- and O-atoms as the system evolves over time t. Our simulations run long enough in order to observe the transition from out-of-equilibrium to equilibrium dynamics. We determine for our system the generalized incoherent intermediate scattering function $C(q,t_{\rm w},t_{\rm w}+t)$ and the dynamic susceptibility $\chi_4(q,t_{\rm w},t_{\rm w}+t)$ where $q$ corresponds to the wavevector. Curves corresponding to different waiting times $t_{\rm w}$ collapse on the scaling plot $\chi_4(q,t_{\rm w},t_{\rm w}+t)/\chi_4^{\rm max}(q,t_{\rm w})$ as a function of $\large (1-C(q,t_{\rm w},t_{\rm w}+t) \large )$, which agrees with a prediction from spin glass theory.