Department of Chemistry, Emory University, 1515 Dickey Drive, Atlanta, Georgia, 30322.
J Comput Chem. 2019 Jan 5;40(1):135-147. doi: 10.1002/jcc.25554. Epub 2018 Oct 3.
The partition-enabled analysis of cluster histograms (PEACH) method is used to calculate the free energy surface of NaCl aggregation using cluster statistics from MD simulations of small systems (40-90 ions plus solvent) in four solvents. In all cases (pure methanol, pure water, and two methanol/water mixtures) NaCl clusters show a transition from amorphous to rocksalt structure with increasing cluster size. The crossover sizes, and the apparent kinetic barrier to ordering, increase with increasing water content. Implications for the proposed two-step mechanism of NaCl crystal nucleation (in which the ordered structure emerges from a large disordered cluster), and how this mechanism might depend on solvent and on degree of supersaturation, are discussed. In pure water, nonideal crowding effects that promote clustering are identified from systematic concentration-dependent deviations between simulation results and the PEACH model fit. In contrast, the ability of PEACH to fit aggregation statistics in mixed solvents is consistent with negligible interactions between ions in different clusters. © 2018 Wiley Periodicals, Inc.
使用基于 MD 模拟的小体系（40-90 个离子加溶剂）簇统计数据，通过分区启用的聚类直方图分析（PEACH）方法计算 NaCl 聚集的自由能表面。在所有情况下（纯甲醇、纯水和两种甲醇/水混合物），随着簇尺寸的增加，NaCl 簇从无定形转变为岩盐结构。交叉尺寸以及有序化的表观动力学势垒随含水量的增加而增加。讨论了 NaCl 晶体成核的两步机制（有序结构从大的无序簇中出现）以及该机制如何取决于溶剂和过饱和度，以及在纯水中，通过模拟结果与 PEACH 模型拟合之间的系统浓度依赖性偏差，确定了促进聚类的非理想拥挤效应。相比之下，PEACH 拟合混合溶剂中聚集统计数据的能力与不同簇中离子之间的可忽略不计的相互作用一致。
