The crystallization of methane hydrates via homogeneous nucleation under natural, moderate conditions is of both industrial and scientific relevance, yet still poorly understood. Predicting the nucleation rates at such conditions is notoriously difficult due to high nucleation barriers, and requires, besides an accurate molecular model, enhanced sampling. Here, we apply the transition interface sampling technique, which efficiently computes the exact rate of nucleation by generating ensembles of unbiased dynamical trajectories crossing predefined interfaces located between the stable states. Using an accurate atomistic force field and focusing on specific conditions of 280 K and 500 bar, we compute for nucleation directly into the sI crystal phase at a rate of ∼10^–17 nuclei per nanosecond per simulation volume or ∼10² nuclei per second per cm³, in agreement with consensus estimates for nearby conditions. As this is most likely fortuitous, we discuss the causes of the large differences between our results and previous simulation studies. Our work shows that it is now possible to compute rates for methane hydrates at moderate supersaturation, without relying on any assumptions other than the force field.

中文翻译：

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使用过渡界面采样的中度过饱和甲烷水合物均相成核速率预测。

在自然，适度的条件下通过均相成核形成甲烷水合物的结晶具有工业和科学意义，但仍知之甚少。由于高的成核屏障，在这样的条件下预测成核速率非常困难，除了精确的分子模型外，还需要增强采样。在这里，我们采用过渡界面采样技术，该技术通过生成跨越稳定状态之间的预定义界面的无偏动态轨迹的集合，有效地计算出精确的成核速率。使用精确的原子力场并关注280 K和500 bar的特定条件，我们以〜10 ^–17的速率直接计算成sI晶相的成核每个模拟体积每纳秒的原子核数或每cm ³每秒约10 ^2个核子数，与附近条件的一致估计一致。由于这很可能是偶然的，因此我们讨论了结果与先前的模拟研究之间存在较大差异的原因。我们的工作表明，现在可以计算中等过饱和度下甲烷水合物的速率，而无需依赖力场以外的任何假设。