Matuszak Daniel, Aranovich Gregory L, Donohue Marc D
Department of Chemical and Biomolecular Engineering, The Johns Hopkins University, Baltimore, MD 21218, USA.
Phys Chem Chem Phys. 2006 Apr 14;8(14):1663-74. doi: 10.1039/b516036g. Epub 2006 Feb 23.
The dependence of the diffusivity on temperature, pressure, and composition is not understood well; consequently, data is preferred significantly over correlations in most practical situations. Even in dilute gases, the contributions of attractions and repulsions to the diffusivity are difficult to understand on a molecular level without performing simulations. We have developed a Lattice Density Functional Theory (LDFT) approach for modeling diffusion to supplement existing methods that are very rigorous but computationally demanding. The LDFT approach is analogous to the van der Waals equation in how it accounts for molecular interactions in that it has first-order corrections to ideal behavior; it is an extension of the Equilibrium LDFT for adsorption and phase behavior. In this work, the LDFT approach is presented and demonstrated by modeling the problem of color counterdiffusion in an externally-applied potential field. This potential field, in combination with the intermolecular potential function, creates a diffusion regime in which repulsions cause oscillations in the density profile. Using the LDFT approach, the oscillations were described and attributed to nearest-neighbor and next nearest-neighbor interactions. The LDFT approach gives qualitative and quantitative agreement with dual control-volume Grand Canonical Molecular Dynamics simulations.
扩散系数对温度、压力和组成的依赖性尚未得到很好的理解；因此，在大多数实际情况下，数据比相关性更受青睐。即使在稀薄气体中，如果不进行模拟，在分子层面上，吸引力和排斥力对扩散系数的贡献也很难理解。我们已经开发了一种用于模拟扩散的晶格密度泛函理论（LDFT）方法，以补充现有的非常严格但计算要求很高的方法。LDFT方法在解释分子相互作用方面类似于范德华方程，因为它对理想行为有一阶修正；它是用于吸附和相行为的平衡LDFT的扩展。在这项工作中，通过对外部施加势场中的颜色反向扩散问题进行建模，展示了LDFT方法。这个势场与分子间势函数相结合，创建了一个扩散区域，其中排斥力导致密度分布出现振荡。使用LDFT方法，描述了这些振荡并将其归因于最近邻和次近邻相互作用。LDFT方法与双控制体积巨正则分子动力学模拟在定性和定量上都一致。
