Examination of dynamic facilitation in molecular dynamics simulations of glass-forming liquids

Using data from molecular dynamics computer simulations of the one-component Dzugutov liquid and of BKS silica in metastable equilibrium supercooled states, we examine ideas introduced by Garrahan and Chandler (GC) in their dynamic facilitation (DF) model of the glass transition. Utilizing a recently introduced measure of DF, we find that DF is important for particle motion in both the supercooled Dzugutov liquid and in the BKS silica melt, that mobility propagates continuously, and that this effect becomes increasingly pronounced with decreasing T. We show that, in both systems, dynamic facilitation is strongest on the time scale of the late-beta relaxation, where clusters of highly mobile neighboring particles escaping from their cages are largest and, except for the silicon atoms in BKS silica, stringlike motion is most prominent. By comparing the two systems, we show that the temperature dependence of one measure of DF as the mode-coupling temperature is approached from high temperature is similar, once the temperature dependence of the structural relaxation time in each system is scaled out.