School of Physical Sciences, Jawaharlal Nehru University, New Delhi 110067, India.
J Chem Phys. 2012 Jul 14;137(2):024508. doi: 10.1063/1.4731705.
The relationships between diffusivity and the excess, pair and residual multiparticle contributions to the entropy are examined for Lennard-Jones liquids and binary glassformers, in the context of approximate inverse power law mappings of simple liquids. In the dense liquid where diffusivities are controlled by collisions and cage relaxations, Rosenfeld-type excess entropy scaling of diffusivities is found to hold for both crystallizing as well as vitrifying liquids. The crucial differences between the two categories of liquids emerge only when local cooperative effects in the dynamics result in significant caging effects in the time-dependent behaviour of the single-particle mean square displacement. In the case of glassformers, onset of such local cooperativity coincides with onset of deviations from Rosenfeld-type excess entropy scaling of diffusivities and increasing spatiotemporal heterogeneity. In contrast, for two- and three-dimensional liquids with a propensity to crystallise, the onset of local cooperative dynamics is sufficient to trigger crystallization provided that the liquid is sufficiently supercooled that the free energy barrier to nucleation of the solid phase is negligible. The state points corresponding to onset of transient caging effects can be associated with typical values, within reasonable bounds, of the excess, pair, and residual multiparticle entropy as a consequence of the isomorph-invariant character of the excess entropy, diffusivity and related static and dynamic correlation functions.
本文研究了在简单液体的近似逆幂律映射的背景下，扩散系数与过剩、配对和剩余多粒子对熵的贡献之间的关系，研究对象为 Lennard-Jones 液体和二元玻璃形成体。在密集液体中，扩散系数受碰撞和笼松弛控制，发现对于结晶液体和玻璃化液体，Rosenfeld 型过剩熵对扩散系数的标度都成立。只有当动力学中的局部协同效应导致单粒子均方位移的时变行为中出现显著的笼效应时，两种液体之间才会出现关键差异。对于玻璃形成体，这种局部协同作用的出现与扩散系数的 Rosenfeld 型过剩熵标度偏离以及时空异质性增加的出现相一致。相比之下，对于具有结晶倾向的二维和三维液体，只要液体过冷度足够大，固相成核的自由能势垒可以忽略不计，局部协同动力学的出现足以引发结晶。由于过剩熵、扩散系数以及相关静态和动态相关函数的同形态不变性特征，与瞬态笼效应出现相关的状态点可以与过剩、配对和剩余多粒子熵的典型值相关联，在合理范围内。
