Coslovich D, Pastore G
Institut für Theoretische Physik and CMS, Technische Universität Wien, Wiedner Hauptstraße 8-10, A-1040 Wien, Austria.
J Phys Condens Matter. 2009 Jul 15;21(28):285107. doi: 10.1088/0953-8984/21/28/285107. Epub 2009 Jun 19.
We report molecular dynamics simulations for a new model of tetrahedral network glass-former, based on short-range spherical potentials. Despite the simplicity of the forcefield employed, our model reproduces some essential physical properties of silica, an archetypal network-forming material. Structural and dynamical properties, including dynamic heterogeneities and the nature of local rearrangements, are investigated in detail and a direct comparison with models of close-packed, fragile glass-formers is performed. The outcome of this comparison is rationalized in terms of the properties of the potential energy surface, focusing on the unstable modes of the stationary points. Our results indicate that the weak degree of dynamic heterogeneity observed in network glass-formers may be attributed to an excess of localized unstable modes, associated with elementary dynamical events such as bond breaking and reformation. In contrast, the more fragile Lennard-Jones mixtures are characterized by a larger fraction of extended unstable modes, which lead to a more cooperative and heterogeneous dynamics.
我们报告了基于短程球形势的四面体网络玻璃形成体新模型的分子动力学模拟。尽管所采用的力场很简单，但我们的模型再现了二氧化硅（一种典型的网络形成材料）的一些基本物理性质。详细研究了结构和动力学性质，包括动态非均匀性和局部重排的性质，并与密堆积的、易碎的玻璃形成体模型进行了直接比较。根据势能面的性质对这种比较的结果进行了合理化解释，重点关注驻点的不稳定模式。我们的结果表明，在网络玻璃形成体中观察到的动态非均匀性程度较弱可能归因于与键断裂和重新形成等基本动力学事件相关的局部不稳定模式过多。相比之下，更易碎的 Lennard-Jones 混合物的特征是扩展不稳定模式的比例更大，这导致了更协同和非均匀的动力学。
