Honeywell Process Solutions, 300-250 York St., London, Ontario N6A 6K2, Canada.
J Chem Phys. 2012 Jan 21;136(3):034505. doi: 10.1063/1.3677193.
First-order phase transitions of binary mixtures at the given pressure (P) and temperature (T) are studied by taking into account the composition fluctuations. Isothermal-isobaric semigrand canonical ensemble is adopted to find the relations among the total number of molecules, the composition fluctuations and Gibbs free energy density. By combining two identical subsystems of mixtures successively, the free energy density is transformed until being stable and its linear segments represent phase transitions. A new method is developed to calculate the phase equilibriums of binary mixtures. The method handles multiple types and number of phase equilibriums at single time and its solutions are physically justified. One example is shown for calculating the phase diagram of binary Lennard-Jones mixture. It demonstrates that the fluctuations of the total number of molecules in mixtures are fundamental behind phase transitions and the van der Waals loops in Gibbs free energy are reasonable.
在给定的压力 (P) 和温度 (T) 下，通过考虑组成波动来研究二元混合物的一级相变。采用等温等压半正则巨正则系综来寻找总分子数、组成波动和吉布斯自由能密度之间的关系。通过连续组合两个相同的混合物子系统，直到自由能密度稳定并呈现线性段，就可以进行相变转换。开发了一种新的方法来计算二元混合物的相平衡。该方法可以在单个时间内处理多种类型和数量的相平衡，并且其解决方案具有物理意义。给出了一个例子来计算二元 Lennard-Jones 混合物的相图。结果表明，混合物中总分子数的波动是相变的基础，吉布斯自由能中的范德华环是合理的。
