水的粗颗粒模型自支撑薄膜中次表面冻结的抑制
Suppression of Sub-surface Freezing in Free-Standing Thin Films of a Coarse-grained Model of Water
摘要：
水-汽界面附近的冻结现象引起了许多学科的极大兴趣，其中最引人注目的是大气科学。在这项工作中，我们使用分子动力学和两个先进的采样技术，前向通量采样和伞采样，研究冰在独立的过冷水薄膜的均匀成核。我们使用一个粗粒度的单原子模型的水，被称为mW，我们发现，在这个模型中的汽-液界面抑制在其附近的结晶。这种抑制发生在平坦界面附近，在那里没有净拉普拉斯压力的诱导。我们的自由能计算表明，出现在界面附近的临界前晶核的稳定性比那些出现在散装。我们通过计算在膜的不同区域形成的核的平均非球面度来研究这种不稳定性的起源，并观察到平均非球面度在更靠近界面处增加，这与由于增加的表面-体积比而增加的自由能一致。
英文摘要：
Freezing in the vicinity of water-vapor interfaces is of considerable interest to a wide range of disciplines, most notably the atmospheric sciences. In this work, we use molecular dynamics and two advanced sampling techniques, forward flux sampling and umbrella sampling, to study homogeneous nucleation of ice in free-standing thin films of supercooled water. We use a coarse-grained monoatomic model of water, known as mW, and we find that in this model a vapor-liquid interface suppresses crystallization in its vicinity. This suppression occurs in the vicinity of flat interfaces where no net Laplace pressure in induced. Our free energy calculations reveal that the pre-critical crystalline nuclei that emerge near the interface are thermodynamically less stable than those that emerge in the bulk. We investigate the origin of this instability by computing the average asphericity of nuclei that form in different regions of the film, and observe that average asphericity increases closer to the interface, which is consistent with an increase in the free energy due to increased surface-to-volume ratios.
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