Department of Physics, University of Bath, Bath BA2 7AY, United Kingdom.
J Chem Phys. 2010 Nov 21;133(19):194102. doi: 10.1063/1.3495996.
Highly size-asymmetrical fluid mixtures arise in a variety of physical contexts, notably in suspensions of colloidal particles to which much smaller particles have been added in the form of polymers or nanoparticles. Conventional schemes for simulating models of such systems are hamstrung by the difficulty of relaxing the large species in the presence of the small one. Here we describe how the rejection-free geometrical cluster algorithm of Liu and Luijten [J. Liu and E. Luijten, Phys. Rev. Lett. 92, 035504 (2004)] can be embedded within a restricted Gibbs ensemble to facilitate efficient and accurate studies of fluid phase behavior of highly size-asymmetrical mixtures. After providing a detailed description of the algorithm, we summarize the bespoke analysis techniques of [Ashton et al., J. Chem. Phys. 132, 074111 (2010)] that permit accurate estimates of coexisting densities and critical-point parameters. We apply our methods to study the liquid-vapor phase diagram of a particular mixture of Lennard-Jones particles having a 10:1 size ratio. As the reservoir volume fraction of small particles is increased in the range of 0%-5%, the critical temperature decreases by approximately 50%, while the critical density drops by some 30%. These trends imply that in our system, adding small particles decreases the net attraction between large particles, a situation that contrasts with hard-sphere mixtures where an attractive depletion force occurs.
高度尺寸不对称的流体混合物出现在各种物理环境中，特别是在胶体颗粒悬浮液中，其中添加了更小的颗粒，如聚合物或纳米颗粒。模拟此类系统模型的传统方案受到在存在小颗粒的情况下难以松弛大颗粒的限制。在这里，我们描述了如何将 Liu 和 Luijten 的无排斥几何簇算法[J. Liu 和 E. Luijten, Phys. Rev. Lett. 92, 035504 (2004)]嵌入受限 Gibbs 系综中，以促进对高度尺寸不对称混合物的流体相行为的有效和准确研究。在提供算法的详细描述之后，我们总结了[Ashton 等人，J. Chem. Phys. 132, 074111 (2010)]的定制分析技术，这些技术允许对共存密度和临界点参数进行准确估计。我们应用我们的方法来研究具有 10:1 尺寸比的特定 Lennard-Jones 粒子混合物的液-气相图。随着小颗粒的储层体积分数在 0%-5%的范围内增加，临界温度降低约 50%，而临界密度下降约 30%。这些趋势表明，在我们的系统中，添加小颗粒会降低大颗粒之间的净吸引力，这种情况与硬球混合物相反，硬球混合物中存在吸引力耗尽力。
