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arXiv 1301.7019cond-mat.stat-mech
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玻璃化转变的伊辛模型

Ising Model of a Glass Transition

J. S. Langer

摘要:

田中和同事的数值模拟表明,玻璃形成系统的适度多分散的硬核颗粒,在二维和三维,表现出发散的相关长度。这些相关性描述的伊辛样临界指数,并与发散,Vogel-Fulcher-Tamann,结构弛豫时间。热化硬盘的相关模拟表明,不同的多分散性的压力与包装分数的曲线表现出一系列的过渡点,开始与液体六角过渡的单分散的情况下,和交叉与增加多分散性的玻璃,伊辛样临界点。我建议解释这些观察假设,玻璃形成流体包含双重退化,局部有序的粒子簇,类似的两个状态的系统,已被调用来解释其他玻璃现象。本文首先从一个简短的统计推导热力学的热化,硬核粒子。然后,它讨论了一个两个状态,伊辛样模型可以在该框架内描述的统计相关的,内部状态变量的一个小数目。所得理论与模拟数据吻合得很好。我还提出了一个理由观察到的伊辛样相关长度和Vogel-Fulcher-Tamann公式之间的关系。

英文摘要:

Numerical simulations by Tanaka and coworkers indicate that glass forming systems of moderately polydisperse hard-core particles, in both two and three dimensions, exhibit diverging correlation lengths. These correlations are described by Ising-like critical exponents, and are associated with diverging, Vogel-Fulcher-Tamann, structural relaxation times. Related simulations of thermalized hard disks indicate that the curves of pressure versus packing fraction for different polydispersities exhibit a sequence of transition points, starting with a liquid-hexatic transition for the monodisperse case, and crossing over with increasing polydispersity to glassy, Ising-like critical points. I propose to explain these observations by assuming that glass-forming fluids contain twofold degenerate, locally ordered clusters of particles, similar to the two-state systems that have been invoked to explain other glassy phenomena. This paper starts with a brief statistical derivation of the thermodynamics of thermalized, hard-core particles. It then discusses how a two-state, Ising-like model can be described within that framework in terms of a small number of statistically relevant, internal state variables. The resulting theory agrees accurately with the simulation data. I also propose a rationale for the observed relation between the Ising-like correlation lengths and the Vogel-Fulcher-Tamann formula.

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