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arXiv 1802.00645cond-mat.soft
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稠密二维平衡液体中结构动力学异质性的定量计算

Quantifying Structural Dynamic Heterogeneity in a Dense Two-dimensional Equilibrium Liquid

Tamoghna Das, Jack F. Douglas

摘要:

我们研究了模型平衡流体的局部结构波动,目的是更好地理解最近对玻璃形成液体和其他强相互作用粒子系统(如脂质膜、尘埃等离子体、晶体界面动力学、蛋白质内部动力学等)的模拟和实验研究中确定的局部非均匀动力学的结构基础。我们用分子动力学模拟研究了二维单组分Lennard-Jones在一定密度和温度范围内的液晶和结晶相。我们通过基于立体角的曲面细分技术检查单个粒子的紧邻区域来识别三种不同的粒子结构类别。特别是,区域分布的社区揭示了具有六边形,五边形和正方形对称的笼子。在液相中,五边形单元似乎是主要的基序,而在完美晶体的情况下,固相是由六边形单元占主导地位。分别检查属于每个结构类的颗粒的空间组织表明,由在液体和固体内发现的六边形和五边形群体的颗粒形成的有限大小的簇,分别以互补的方式作为密度的函数生长,并且两种颗粒群体在液晶共存制度内渗透。有趣的是,不同的局部结构的粒子的人口,由相邻粒子的排列定义,被发现保持不同的扩散率计算的组成粒子的速度自相关的所有密度研究。我们的分析提供了一个新的分析方法和一个可能的框架,了解软材料的结构变化。

英文摘要:

We investigate the local structural fluctuations of a model equilibrium fluid with an aim of better understanding the structural basis of locally heterogeneous dynamics identified in recent simulations and experimental studies of glass-forming liquids and other strongly interacting particle systems, such as, lipid membranes, dusty plasmas, interfacial dynamics of crystals, internal dynamics of proteins, etc. In particular, we study a two-dimensional single component Lennard-Jones over a range of densities and constant temperature covering both the liquid and crystalline phase by molecular dynamics simulation. We identify three distinct structural classes of particles by examining the immediate neighborhood of individual particles based on a solid-angle based tessellation technique. In particular, the area distribution of the neighborhoods reveals cages having hexagonal, pentagonal and square symmetries. Pentagonal cells appear to be predominant motif in the liquid phase, while the solid phase is dominated by hexagonal cells, as in the case of the perfect crystal. Examining the spatial organization of particles belonging to each structural class separately shows that finite-size clusters formed by particles of hexagonal and pentagonal population found within liquids and solids, respectively, grow in a complementary way as a function of density and both particle populations percolate within liquid-crystal coexistence regime. Interestingly, the populations of particles with different local structures, defined by the arrangement of neighboring particles, are found to maintain different diffusivity computed from the velocity autocorrelation of constituent particles for all densities studied. Our analysis provides a new approach for analyzing and a possible framework for understanding the structural changes in soft materials.

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