School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York 14853, USA.
J Chem Phys. 2016 Dec 7;145(21):211903. doi: 10.1063/1.4953862.
The phase behavior and the homogeneous nucleation of an equimolar mixture of octahedra and cuboctahedra are studied using thermodynamic integration, Gibbs-Duhem integration, and umbrella sampling simulations. The components of this mixture are modeled as polybead objects of equal edge lengths so that they can assemble into a space-filling compound with the CsCl crystal structure. Taking as reference the hard-core system where the compound crystal does not spontaneously nucleate, we quantified the effect of inter-species selective interactions on facilitating the disorder-to-order transition. Facet selective and facet non-selective inter-species attractions were considered, and while the former was expectedly more favorable toward the target tessellating structure, the latter was found to be similarly effective in nucleating the crystal compound. Ranges for the strength of attractions and degree of supersaturation were identified where the nucleation free-energy barrier was small enough to foretell a fast process but large enough to prevent spinodal fluctuations that can trap the system in dense metastable states lacking long-range order. At those favorable conditions, the tendency toward the local orientational order favored by packing entropy is amplified and found to play a key role seeding nuclei with the CsCl structure.
使用热力学积分、吉布斯-杜恒积分和伞状采样模拟研究了八面体和立方八面体等摩尔混合物的相行为和均相成核。该混合物的成分建模为具有相等边缘长度的多珠物体，以便它们可以组装成具有 CsCl 晶体结构的空间填充化合物。以不自发成核的硬球系统为参考，我们量化了物种间选择性相互作用对促进无序到有序转变的影响。考虑了面选择性和非面选择性的种间吸引，虽然前者显然更有利于目标镶嵌结构，但后者在成核晶体化合物方面同样有效。确定了吸引力强度和过饱和度的范围，在这些范围内，成核自由能垒足够小，可以预测快速过程，但又足够大，可以防止可能将系统困在缺乏长程有序的密集亚稳状态的旋节线涨落。在那些有利的条件下，由堆积熵引起的局部取向有序的趋势被放大，并发现它在成核 CsCl 结构的核方面起着关键作用。
