University of Puget Sound, Tacoma, Washington 98416, USA.
J Phys Chem A. 2011 Jun 16;115(23):6184-93. doi: 10.1021/jp111359a. Epub 2011 Apr 19.
We present the results of molecular dynamics simulations in which ice I(h) slabs with free basal, prismatic, 28° pyramidal, and 14° pyramidal facets are exposed to vapor. All simulations were carried out at 250 K using a six-site intermolecular potential. Characteristics common to all facets include spontaneous development of a quasi-liquid layer (QLL) within ∼10 ns and QLL stratification into outer (ε(1)) and inner (ε(2)) sublayers having on average two and three hydrogen bonds, respectively. Vapor pressure, based on the rate of escape of molecules from the QLL to the vapor phase, is found to be greatest for the 14° pyramidal and basal facets (∼230 Pa), while significantly lower values are obtained for the prismatic and 28° pyramidal facets (∼200 Pa). The geometric thickness of the QLL also varies between facets, with the 14° pyramidal having the greatest thickness. The free prismatic and pyramidal facets exhibit significant anisotropic diffusivity, in-plane motion being faster in the trans-prismatic direction than in the basal-to-basal direction. The in-plane diffusion length is greatest for the 28° pyramidal facet and smallest for the prismatic facet. This diversity of facet-specific properties provides a rich set of possibilities for mechanisms of ice crystal growth and ablation.
我们呈现了分子动力学模拟的结果，其中暴露于蒸汽的冰 Ih 片具有自由的基面、棱柱面、28°棱锥面和 14°棱锥面。所有模拟均在 250 K 下使用六位点分子间势能进行。所有面都具有的特征包括在大约 10 ns 内自发形成准液相层（QLL），并且 QLL 分层为具有平均两个和三个氢键的外层（ε(1)）和内层（ε(2)）。基于分子从 QLL 逸出到气相的速率，发现 14°棱锥面和基面的蒸汽压最大（约 230 Pa），而棱柱面和 28°棱锥面的蒸汽压显著较低（约 200 Pa）。QLL 的几何厚度也在面之间变化，其中 14°棱锥面具有最大的厚度。自由的棱柱面和棱锥面表现出显著的各向异性扩散性，在横向棱柱方向上的运动比在基面到基面方向上的运动更快。28°棱锥面的面内扩散长度最大，棱柱面的最小。这种特定于面的性质的多样性为冰晶生长和消融的机制提供了丰富的可能性。
