School of Design, Engineering and Computing, Bournemouth University, Poole House, Talbot Campus, Poole, Dorset BH12 5BB, United Kingdom.
J Chem Phys. 2010 Feb 14;132(6):064504. doi: 10.1063/1.3319510.
Thermodynamic stability of model single component and binary mixture fluids is considered with the Fisher-Ruelle (FR) stability criteria, which apply in the thermodynamic limit, and molecular dynamics (MD) simulation for finite periodic systems. Two soft-core potential forms are considered, phi(6,1)(r)=4[1/(a+r(6))(2)-1/(a+r(6))] and phi(2,3)(r)=4[1/(a+r(2))(6)-1/(a+r(2))(3)], where r is the separation between the particle centers. According to FR these are unstable in the thermodynamic limit if a>a(c)=1/2 and a>a(c)=(7/32)(1/3), respectively. MD simulations with single-component particles show, however, that this transition on typical simulation times is more gradual for finite periodic systems with variation in a on either side of a(c). For a<a(c), asymmetric density fluctuations are stabilized by the periodic boundary conditions. Also for binary mixtures of (stable) Lennard-Jones and phi(2,3) particles, phase separation into regions richer in one component than the other was observed for a<a(c). Binary systems with interactions similar to a model polymer-colloid fluid in the "depletion" limit equilibrated particularly slowly for a>a(c), with the unstable component in the mixture breaking up into many long-lived microdroplets which conferred apparent equilibrium thermodynamic behavior (i.e., negligible N-dependence of the average potential energy per particle) in this period.
考虑了模型单组分和二元混合物流体的热力学稳定性，使用了适用于热力学极限的 Fisher-Ruelle（FR）稳定性准则和有限周期性系统的分子动力学（MD）模拟。考虑了两种软核势形式，phi(6,1)(r)=4[1/(a+r(6))(2)-1/(a+r(6))] 和 phi(2,3)(r)=4[1/(a+r(2))(6)-1/(a+r(2))(3)]，其中 r 是粒子中心之间的距离。根据 FR，这些在热力学极限下是不稳定的，如果 a>a(c)=1/2 和 a>a(c)=(7/32)(1/3)，分别。然而，对于单组分粒子的 MD 模拟，对于有限周期性系统，在 a 两侧变化时，这种转变在典型的模拟时间内更加渐进。对于 a<a(c)，不对称密度涨落被周期性边界条件稳定化。对于 Lennard-Jones 和 phi(2,3)粒子的二元混合物，也观察到了在 a<a(c)时，向一个组分比另一个组分更丰富的区域的相分离。在“耗尽”极限下类似于模型聚合物胶体流体相互作用的二元系统，对于 a>a(c)，平衡特别缓慢，混合物中的不稳定组分分解成许多长寿命的微滴，这些微滴赋予了明显的平衡热力学行为（即，每个粒子的平均势能与 N 无关）在这段时间内。
