大平衡：汽液平衡的分子模拟新方法
Grand Equilibrium: vapour-liquid equilibria by a new molecular simulation method
摘要：
本文提出了一种计算混合物汽液平衡的分子模拟新方法。在该方法中，独立的热力学变量是温度和液体组成。在第一步中，进行液相的等压等温模拟，其中所有组分及其导数相对于压力的化学势，即，计算偏摩尔体积。从这些结果，一阶泰勒级数展开的化学势的函数的压力$μ_i(p)$在恒定的液体组成的确定。这一信息是必要的，因为液体中的特定压力通常不等于平衡压力，而平衡压力必须在蒸汽模拟过程中找到。在第二步骤中，进行汽相的一个伪巨正则模拟，其中使用先前确定的函数$μ_i(p^v)$根据瞬时压力$p^v$设置化学势。用这种方法，得到了与给定温度和液体组成相一致的蒸汽压和蒸汽组成的结果，并将这种新方法应用于纯Lennard-Jones流体、二元和三元混合Lennard-Jones球，结果与文献中的相应数据吻合得很好。
英文摘要：
A new molecular simulation method for the calculation of vapour-liquid equilibria of mixtures is presented. In this method, the independent thermodynamic variables are temperature and liquid composition. In the first step, one isobaric isothermal simulation for the liquid phase is performed, in which the chemical potentials of all components and their derivatives with respect to the pressure, i.e., the partial molar volumes, are calculated. From these results, first order Taylor series expansions for the chemical potentials as functions of the pressure $μ_i(p)$ at constant liquid composition are determined. That information is needed, as the specified pressure in the liquid will generally not be equal to the equilibrium pressure, which has to be found in the course of a vapour simulation. In the second step, one pseudo grand canonical simulation for the vapour phase is performed, where the chemical potentials are set according to the instantaneous pressure $p^v$ using the previously determined function $μ_i(p^v)$. In this way, results for the vapour pressure and vapour composition are achieved which are consistent to the given temperature and liquid composition.The new method is applied to the pure Lennard-Jones fluid, a binary, and a ternary mixture of Lennard-Jones spheres and shows very good agreement with corresponding data from the literature.
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