Bergroth Magnus N J, Vogel Michael, Glotzer Sharon C
Departments of Chemical Engineering and Materials Science & Engineering, University of Michigan, Ann Arbor, Michigan 48109-2136, USA.
J Phys Chem B. 2005 Apr 14;109(14):6748-53. doi: 10.1021/jp0447946.
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.
利用单组分祖古托夫液体和处于亚稳平衡过冷状态的BKS二氧化硅的分子动力学计算机模拟数据，我们检验了加拉汉和钱德勒（GC）在其玻璃化转变的动态促进（DF）模型中提出的观点。利用最近引入的DF度量，我们发现DF对过冷祖古托夫液体和BKS二氧化硅熔体中的粒子运动都很重要，迁移率连续传播，并且这种效应随着温度降低而变得越来越明显。我们表明，在这两个系统中，动态促进在晚期β弛豫的时间尺度上最强，此时从其笼中逸出的高度移动的相邻粒子簇最大，并且除了BKS二氧化硅中的硅原子外，线状运动最为突出。通过比较这两个系统，我们表明，一旦消除每个系统中结构弛豫时间的温度依赖性，当从高温接近模式耦合温度时，一种DF度量的温度依赖性是相似的。
