How to quantify and avoid finite size effects in computational studies of crystal nucleation: The case of heterogeneous ice nucleation
How to quantify and avoid finite size effects in computational studies of crystal nucleation: The case of heterogeneous ice nucleation
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DOI：
10.1063/5.0026355
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发表时间：
2021-01-07
影响因子：
4.4
通讯作者：
Haji-Akbari, Amir
中科院分区：
文献类型：
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作者：
Hussain, Sarwar;Haji-Akbari, Amir
晶体成核的计算研究可能受到有限尺寸效应的影响，主要是由于晶核与其周期性图像之间的非物理相互作用。然而，由于成核研究的计算成本很高，系统地研究成核动力学和机理对系统尺寸的敏感性并不总是可行的。在这里，我们使用跳跃向前通量采样，以准确地计算率的非均质冰成核在附近的方形模型无结构的冰成核颗粒（INPs）的不同大小，并确定三个不同的制度的依赖率的INP尺寸，L。对于小的INPs，由于人工跨越周期性边界的临界核，速率是L的强函数。然而，中等大小的INPs引起非跨越的“近端”核的出现，这些核足够接近它们的周期图像以完全构造中间液体。虽然这种接近可以促进成核，但其效果被中间液体的较高密度抵消，导致总体上人为较小的成核速率。在大的INPs形成的临界核既不跨越也不接近。然而，速率是L的弱函数，其对数与1/L成线性比例。从这些观察中出现的关键启发是，如果临界核既不跨越也不接近，并且如果中间液体具有在相同条件下与过冷液体在结构上无法区分的区域，则有限尺寸效应将是最小的。
Computational studies of crystal nucleation can be impacted by finite size effects, primarily due to unphysical interactions between crystalline nuclei and their periodic images. It is, however, not always feasible to systematically investigate the sensitivity of nucleation kinetics and mechanism to system size due to large computational costs of nucleation studies. Here, we use jumpy forward flux sampling to accurately compute the rates of heterogeneous ice nucleation in the vicinity of square-shaped model structureless ice nucleating particles (INPs) of different sizes and identify three distinct regimes for the dependence of rate on the INP dimension, L. For small INPs, the rate is a strong function of L due to the artificial spanning of critical nuclei across the periodic boundary. Intermediate-sized INPs, however, give rise to the emergence of non-spanning "proximal" nuclei that are close enough to their periodic images to fully structure the intermediary liquid. While such proximity can facilitate nucleation, its effect is offset by the higher density of the intermediary liquid, leading to artificially small nucleation rates overall. The critical nuclei formed at large INPs are neither spanning nor proximal. Yet, the rate is a weak function of L, with its logarithm scaling linearly with 1/L. The key heuristic emerging from these observations is that finite size effects will be minimal if critical nuclei are neither spanning nor proximal and if the intermediary liquid has a region that is structurally indistinguishable from the supercooled liquid under the same conditions.