Laghaei Rozita, Eskandari Nasrabad Afshin, Chan Eu Byung
Department of Chemistry, McGill University, 801 Sherbrooke West, Montreal, Quebec H3A 2K6, Canada.
J Chem Phys. 2006 Apr 21;124(15):154502. doi: 10.1063/1.2185643.
In the previous papers applying the generic van der Waals equation of state the mean excluded volume was defined with the contact diameter of particles at which the potential energy is equal to zero-the size parameter in the case of the Lennard-Jones potential. This parameter appears as the upper limit of the integral for the generic van der Waals parameter B (mean excluded volume divided by the density) in the generic van der Waals equation of state. Since the choice is not unique, in this paper we reexamine the manner of defining the upper limit and propose another choice for the upper limit. We also propose an interpretation of the free volume overlap factor alpha appearing in the free volume theory of diffusion and a method of estimating it in terms of the intermolecular potential energy only. It is shown that with the so-estimated free volume overlap factor and the new choice of the upper limit of the integral for B the self-diffusion coefficient in the modified free volume theory of diffusion not only acquires a better accuracy than before, but also becomes calculable in terms of only the intermolecular interaction potential without an adjustable parameter. We also assess some of effective diameters of molecules proposed in the literature for their ability to predict the self-diffusion coefficient within the framework of the modified free volume theory of diffusion.
在之前应用通用范德瓦尔斯状态方程的论文中，平均排斥体积是根据势能等于零时粒子的接触直径来定义的——这是 Lennard-Jones 势情况下的尺寸参数。该参数在通用范德瓦尔斯状态方程中表现为通用范德瓦尔斯参数 B（平均排斥体积除以密度）积分的上限。由于这种选择并非唯一，在本文中我们重新审视定义上限的方式，并提出另一种上限选择。我们还对扩散自由体积理论中出现的自由体积重叠因子α提出一种解释，并提出一种仅根据分子间势能来估计它的方法。结果表明，利用如此估计的自由体积重叠因子以及 B 积分上限的新选择，修正的扩散自由体积理论中的自扩散系数不仅比以前具有更高的精度，而且仅根据分子间相互作用势就可计算，无需可调参数。我们还评估了文献中提出的一些分子有效直径在修正的扩散自由体积理论框架内预测自扩散系数的能力。
