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双中心 Lennard-Jones 流体的自扩散系数:分子模拟与自由体积理论

Self-diffusion coefficient of two-center Lennard-Jones fluids: molecular simulations and free volume theory.

作者信息

Nasrabad Afshin Eskandari

机构信息

Department of Physical Chemistry, School of Chemistry, University of Tehran, Tehran 14155-6455, Iran.

出版信息

J Chem Phys. 2009 Jan 14;130(2):024503. doi: 10.1063/1.3054139.

Abstract

A comprehensive investigation is conducted to study the thermodynamics, structure, and mean free volume of rigid two-center Lennard-Jones fluids through Monte Carlo simulations. For a large number of states, the self-diffusion coefficient is computed using the following two different approaches: the equilibrium molecular dynamics simulation method and the modified Cohen-Turnbull theory. The effects of the bond elongation on different thermophysical properties are studied. The generic van der Waals theory, which has recently been extended to rigid polyatomic fluids [A. Eskandari Nasrabad and R. Laghaei, J. Chem. Phys. 125, 154505 (2006)], is used to compute the mean free volume needed in the modified Cohen-Turnbull theory. The effective site diameter is computed using the virial minimization method and the results are applied within the generic van der Waals theory. The Gibbs ensemble Monte Carlo simulation technique is applied to determine the location of the fluid phase envelope. The NVT Monte Carlo simulation method is then utilized to compute the equation of state and the correlation functions appearing in the generic van der Waals theory. It appears that the logarithm of the mean free volume versus density is almost linear at rho>rho(c) independent of the bond length, which suggests a universal behavior. The self diffusion coefficient results of the modified Cohen-Turnbull theory are analyzed in detail.

摘要

通过蒙特卡罗模拟对刚性双中心 Lennard-Jones 流体的热力学、结构和平均自由体积进行了全面研究。对于大量状态,使用以下两种不同方法计算自扩散系数:平衡分子动力学模拟方法和修正的 Cohen-Turnbull 理论。研究了键伸长对不同热物理性质的影响。最近已扩展到刚性多原子流体的通用范德华理论 [A. Eskandari Nasrabad 和 R. Laghaei,《化学物理杂志》125, 154505 (2006)] 用于计算修正的 Cohen-Turnbull 理论中所需的平均自由体积。使用维里最小化方法计算有效位点直径,并将结果应用于通用范德华理论中。应用吉布斯系综蒙特卡罗模拟技术确定流体相包络的位置。然后利用 NVT 蒙特卡罗模拟方法计算状态方程和通用范德华理论中出现的相关函数。结果表明,在 ρ>ρ(c) 时,平均自由体积的对数与密度几乎呈线性关系,与键长无关,这表明存在普遍行为。对修正的 Cohen-Turnbull 理论的自扩散系数结果进行了详细分析。

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