Auer S, Frenkel D
FOM Institute for Atomic and Molecular Physics, Amsterdam, The Netherlands.
Nature. 2001 Feb 22;409(6823):1020-3. doi: 10.1038/35059035.
Crystal nucleation is a much-studied phenomenon, yet the rate at which it occurs remains difficult to predict. Small crystal nuclei form spontaneously in supersaturated solutions, but unless their size exceeds a critical value--the so-called critical nucleus--they will re-dissolve rather than grow. It is this rate-limiting step that has proved difficult to probe experimentally. The crystal nucleation rate depends on Pcrit, the (very small) probability that a critical nucleus forms spontaneously, and on a kinetic factor (kappa) that measures the rate at which critical nuclei subsequently grow. Given the absence of a priori knowledge of either quantity, classical nucleation theory is commonly used to analyse crystal nucleation experiments, with the unconstrained parameters adjusted to fit the observations. This approach yields no 'first principles' prediction of absolute nucleation rates. Here we approach the problem from a different angle, simulating the nucleation process in a suspension of hard colloidal spheres, to obtain quantitative numerical predictions of the crystal nucleation rate. We find large discrepancies between the computed nucleation rates and those deduced from experiments: the best experimental estimates of Pcrit seem to be too large by several orders of magnitude.
晶体成核是一个被广泛研究的现象，但其发生速率仍然难以预测。小的晶核在过饱和溶液中自发形成，但除非它们的尺寸超过一个临界值——即所谓的临界核——否则它们会重新溶解而不是生长。正是这个限速步骤在实验上难以探究。晶体成核速率取决于Pcrit，即临界核自发形成的（非常小的）概率，以及一个动力学因子（κ），该因子衡量临界核随后生长的速率。鉴于对这两个量都缺乏先验知识，经典成核理论通常用于分析晶体成核实验，通过调整无约束参数来拟合观测结果。这种方法无法对绝对成核速率进行“第一性原理”预测。在这里，我们从一个不同的角度来处理这个问题，模拟硬胶体球悬浮液中的成核过程，以获得晶体成核速率的定量数值预测。我们发现计算出的成核速率与从实验推导出来的成核速率之间存在很大差异：对Pcrit的最佳实验估计似乎大了几个数量级。
