An integral equation theory for inhomogeneous molecular fluids: the reference interaction site model approach.
An integral equation theory for inhomogeneous molecular fluids: the reference interaction site model approach.
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DOI：
10.1063/1.2819487
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发表时间：
2008-01
期刊：
影响因子：
--
通讯作者：
R. Ishizuka;S. Chong;F. Hirata
中科院分区：
文献类型：
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作者：
R. Ishizuka;S. Chong;F. Hirata
提出了一种适用于非均质分子液体的积分方程组理论。本文导出的“非均质参考相互作用位模型(RISM)”方程是RISM方程在非均质体系中的自然推广。这一理论使得计算位于不同密度区域的两个分子之间的对关联函数成为可能。我们还提出了关于非均质分子液体的闭合关系和分子内磁化率的近似公式。作为理论的初步应用，研究了离子周围的水合结构。选择锂、钠和钾阳离子作为溶质。利用Percus技巧，用RISM理论计算出的溶质-溶剂对关联函数来表示离子周围溶剂的局域密度。然后，我们通过三重关联函数分析了离子周围的水化结构，该三重关联函数由非均匀对关联函数和溶剂的局域密度定义。阳离子三重态关联函数的结果表明，水化壳层的热涨落与溶质离子的大小密切相关。并与柯克伍德叠加近似的三重态关联函数进行了比较，柯克伍德叠加近似用齐次关联代替了非齐次的对关联。对于锂离子，本理论计算的三重态关联函数的行为与柯克伍德近似下计算的结果有显著差异。
An integral equation theory which is applicable to inhomogeneous molecular liquids is proposed. The "inhomogeneous reference interaction site model (RISM)" equation derived here is a natural extension of the RISM equation to inhomogeneous systems. This theory makes it possible to calculate the pair correlation function between two molecules which are located at different density regions. We also propose approximations concerning the closure relation and the intramolecular susceptibility of inhomogeneous molecular liquids. As a preliminary application of the theory, the hydration structure around an ion is investigated. Lithium, sodium, and potassium cations are chosen as the solute. Using the Percus trick, the local density of solvent around an ion is expressed in terms of the solute-solvent pair correlation function calculated from the RISM theory. We then analyze the hydration structure around an ion through the triplet correlation function which is defined with the inhomogeneous pair correlation function and the local density of the solvent. The results of the triplet correlation functions for cations indicate that the thermal fluctuation of the hydration shell is closely related to the size of the solute ion. The triplet correlation function from the present theory is also compared with that from the Kirkwood superposition approximation, which substitutes the inhomogeneous pair correlation by the homogeneous one. For the lithium ion, the behavior of the triplet correlation functions from the present theory shows marked differences from the one calculated within the Kirkwood approximation.