Molecular Thermodynamics and Modeling of Materials Laboratory, Institute of Physical Chemistry, National Center for Scientific Research Demokritos, GR-153 10 Aghia Paraskevi Attikis, Greece.
J Chem Phys. 2010 Dec 14;133(22):224901. doi: 10.1063/1.3506576.
We present a semigrand ensemble Monte Carlo and Brownian dynamics simulation study of structural and dynamical properties of polydisperse soft spheres interacting via purely repulsive power-law potentials with a varying degree of "softness." Comparisons focus on crystal and amorphous phases at their coexistence points. It is shown through detailed structural analysis that as potential interactions soften, the "quality of crystallinity" of both monodisperse and polydisperse systems deteriorates. In general, polydisperse crystalline phases are characterized by a more ordered structure than the corresponding monodisperse ones (i.e., for the same potential softness). This counter-intuitive feature originates partly from the fact that particles of different sizes may be accommodated more flexibly in a crystal structure and from the reality that coexistence (osmotic) pressure is substantially higher for polydisperse systems. These trends diminish for softer potentials. Potential softness eventually produces substitutionally disordered crystals. However, substitutional order is apparent for the hard-spherelike interactions. Diffusionwise, crystals appear quite robust with a slight difference in the vibrational amplitudes of small and large particles. This difference, again, diminishes with potential softness. Overcrowding in amorphous polydisperse suspensions causes "delayed" diffusion at intermediate times.
我们提出了一种半巨正则系综蒙特卡罗和布朗动力学模拟研究，研究了通过具有不同程度“柔软性”的纯排斥幂律势相互作用的多分散软球的结构和动力学性质。比较的重点是共存点处的晶体和非晶相。通过详细的结构分析表明，随着潜在相互作用的软化，单分散和多分散系统的“结晶质量”都恶化了。一般来说，多分散晶体相的结构比相应的单分散相更有序（即对于相同的潜在柔软性）。这种违反直觉的特征部分源于这样一个事实，即不同大小的颗粒在晶体结构中可能更灵活地适应，并且共存（渗透压）压力对于多分散系统要高得多。这些趋势在较软的势下减小。潜在的柔软性最终会产生取代无序的晶体。然而，对于硬球样相互作用，取代序是明显的。在扩散方面，晶体表现出相当的稳健性，只有大小颗粒的振动幅度略有不同。同样，这种差异随着势的软化而减小。在多分散的无定形悬浮液中过度拥挤会导致中间时间的“延迟”扩散。
