Department of Chemistry, Duke University, Durham, North Carolina 27708, USA.
J Chem Phys. 2012 Jun 7;136(21):214106. doi: 10.1063/1.4723869.
Certain models with purely repulsive pair interactions can form cluster crystals with multiply-occupied lattice sites. Simulating these models' equilibrium properties is, however, quite challenging. Here, we develop an expanded isothermal-isobaric [N]pT ensemble that surmounts this problem by allowing both particle number and lattice spacing to fluctuate. It is particularly efficient at high T, where particle insertion is facile. Using this expanded ensemble and thermodynamic integration, we solve the phase diagram of a prototypical cluster-crystal former, the penetrable sphere model, and compare the results with earlier theoretical predictions. At high temperatures and densities, the equilibrium occupancy n(c)(eq) of face-centered cubic crystal increases linearly. At low temperatures, although n(c)(eq) plateaus at integer values, the crystal behavior changes continuously with density. The previously ambiguous crossover around T ~ 0.1 is resolved.
某些具有纯排斥相互作用的模型可以形成占据多个晶格位置的团簇晶体。然而，模拟这些模型的平衡性质是相当具有挑战性的。在这里，我们开发了一个扩展的等温和等压 [N]pT 系综，通过允许粒子数和晶格间距都发生波动来克服这个问题。它在高温下特别有效，因为粒子插入很容易。使用这个扩展系综和热力学积分，我们解决了一个典型的团簇晶体形成体，可穿透球体模型的相图，并将结果与早期的理论预测进行了比较。在高温和高密度下，面心立方晶体的平衡占据数 n(c)(eq) 呈线性增加。在低温下，尽管 n(c)(eq) 在整数处达到平台值，但晶体行为随密度连续变化。之前在 T~0.1 左右的不明确的交叉得到了解决。
