A simulation study of the low temperature phase diagram of the methane monolayer on graphite: a test of potential energy functions.,Physical Chemistry Chemical Physics

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A simulation study of the low temperature phase diagram of the methane monolayer on graphite: a test of potential energy functions.
Physical Chemistry Chemical Physics ( IF 2.9 ) Pub Date : 2020-07-14 , DOI: 10.1039/d0cp02720k
Han Zhang ₁ , Shiliang Johnathan Tan , Luisa Prasetyo , D D Do , D Nicholson

Affiliation

We have used molecular simulation with two intermolecular potential models, TraPPE-UA and TraPPE-EH, the latter of which accounts for the tetrahedral shape, to study the effects of shape on methane adsorption on graphite. Both models give good descriptions of the vapour–liquid equilibria in the bulk phase, but adsorption on graphite is better described by the TraPPE-EH model. Molecular configurations in the monolayer, show the variation with temperature of the registry sites for the carbon and hydrogen atoms of the methane molecules. At temperatures below 70 K, the centre of mass (COM) of the molecules is in registry with the centre of the carbon hexagons. For temperatures above 70 K, a commensurate monolayer is initially formed as at low temperatures, then as the loading is increased the first layer remains in registry, but the COM of the methane molecules in the first layer shifts to the top of the graphite carbon atoms with the C–H bond pointing to carbon atoms in the second shell of a C-hexagon. At temperatures above 93 K, the first adsorbate layer goes through these two commensurate states and then undergoes a transition to an incommensurate solid. Finally, for temperatures greater than 110 K methane behaves like a pseudo spherical molecule.

中文翻译：

石墨上甲烷单层的低温相图的模拟研究：势能函数的测试。

我们使用分子模拟与两个分子间电势模型TraPPE-UA和TraPPE-EH（后者解释了四面体形状）来研究形状对甲烷对石墨吸附的影响。两种模型都很好地描述了本体相中的汽-液平衡，但是TraPPE-EH模型可以更好地描述在石墨上的吸附。单分子层中的分子构型显示出甲烷分子碳原子和氢原子的配准位点随温度的变化。在低于70 K的温度下，分子的质心（COM）与碳六边形的中心对齐。对于高于70 K的温度，最初会在低温下形成相应的单层，然后随着载荷的增加，第一层仍保持配准状态，但是第一层中甲烷分子的COM移到了石墨碳原子的顶部，而C–H键指向C-六边形第二壳中的碳原子。在高于93 K的温度下，第一被吸附物层经历这两个相称的状态，然后转变为不相称的固体。最后，温度高于110 K时，甲烷的行为类似于假球形分子。

更新日期：2020-08-05

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