Scheiner Brett, Yoon Tae Jun
Los Alamos National Laboratory, Los Alamos, New Mexico 87544, USA.
J Chem Phys. 2021 Apr 7;154(13):134101. doi: 10.1063/5.0045211.
This paper presents an application of mean force kinetic theory (MFT) to the calculation of the self-diffusivity of CO in the supercritical fluid regime. Two modifications to the typical application of MFT are employed to allow its application to a system of molecular species. The first is the assumption that the inter-particle potential of mean force can be obtained from the molecule center-of-mass pair correlation function, which in the case of CO is the C-C pair correlation function. The second is a new definition of the Enskog factor that describes the effect of correlations at the surface of the collision volume. The new definition retains the physical picture that this quantity represents a local density increase, resulting from particle correlations, relative to that in the zero density homogeneous fluid limit. These calculations are facilitated by the calculation of pair correlation functions from molecular dynamics (MD) simulations using the FEPM2 molecular CO model. The self-diffusivity calculated from theory is in good agreement with that from MD simulations up to and slightly beyond the density at the location of the Frenkel line. The calculation is compared with and is found to perform similarly well to other commonly used models but has a greater potential for application to systems of mixed species and to systems of particles with long range interatomic potentials due to electrostatic interactions.
本文介绍了平均力动力学理论（MFT）在超临界流体区域中一氧化碳自扩散系数计算方面的应用。对MFT的典型应用进行了两项修改，以使其适用于分子物种系统。第一项是假设平均力的粒子间势可以从分子质心对关联函数中获得，对于一氧化碳而言，就是C-C对关联函数。第二项是对恩斯科格因子的新定义，该因子描述了碰撞体积表面相关性的影响。新定义保留了这样的物理图像：该量表示由于粒子相关性导致的相对于零密度均匀流体极限下局部密度的增加。通过使用FEPM2分子一氧化碳模型从分子动力学（MD）模拟中计算对关联函数，这些计算变得更加容易。从理论计算得到的自扩散系数与MD模拟结果在弗伦克尔线位置处的密度及略高于该密度的范围内吻合良好。将该计算与其他常用模型进行了比较，发现其表现同样出色，但由于静电相互作用，它在应用于混合物种系统和具有长程原子间势的粒子系统方面具有更大的潜力。
