Université Montpellier 2, Laboratoire Charles Coulomb UMR 5221, Montpellier, France.
J Chem Phys. 2012 Nov 14;137(18):184904. doi: 10.1063/1.4765704.
We present molecular dynamics (MD) simulations results for dense fluids of ultrasoft, fully penetrable particles. These are a binary mixture and a polydisperse system of particles interacting via the generalized exponential model, which is known to yield cluster crystal phases for the corresponding monodisperse systems. Because of the dispersity in the particle size, the systems investigated in this work do not crystallize and form disordered cluster phases. The clustering transition appears as a smooth crossover to a regime in which particles are mostly located in clusters, isolated particles being infrequent. The analysis of the internal cluster structure reveals microsegregation of the big and small particles, with a strong homo-coordination in the binary mixture. Upon further lowering the temperature below the clustering transition, the motion of the clusters' centers-of-mass slows down dramatically, giving way to a cluster glass transition. In the cluster glass, the diffusivities remain finite and display an activated temperature dependence, indicating that relaxation in the cluster glass occurs via particle hopping in a nearly arrested matrix of clusters. Finally we discuss the influence of the microscopic dynamics on the transport properties by comparing the MD results with Monte Carlo simulations.
我们呈现了稠密流体中超软、完全可穿透粒子的分子动力学（MD）模拟结果。这些是通过广义指数模型相互作用的二元混合物和多分散体系，该模型已知对应于单分散体系会产生团簇晶体相。由于颗粒尺寸的分散性，本工作中研究的系统不会结晶形成无序团簇相。聚类转变表现为一个平滑的转变，在此转变中，粒子主要位于团簇中，孤立的粒子很少。对内部团簇结构的分析揭示了大颗粒和小颗粒的微分离，在二元混合物中存在强烈的同配位。当温度进一步降低到聚类转变以下时，团簇质心的运动显著减慢，导致团簇玻璃转变。在团簇玻璃中，扩散系数保持有限并显示出激活温度依赖性，表明团簇玻璃中的弛豫是通过粒子在几乎停滞的团簇基质中的跳跃来实现的。最后，我们通过将 MD 结果与蒙特卡罗模拟进行比较，讨论了微观动力学对输运性质的影响。
