Desgranges Caroline, Delhommelle Jerome
Department of Chemistry, University of North Dakota, 151 Cornell Street Stop 9024, Grand Forks, North Dakota 58202, USA.
J Chem Phys. 2014 Mar 14;140(10):104109. doi: 10.1063/1.4867498.
Combining rules, such as the Lorentz-Berthelot rules, are routinely used to calculate the thermodynamic properties of mixtures using molecular simulations. Here we extend the expanded Wang-Landau simulation approach to determine the impact of the combining rules on the value of the partition function of binary systems, and, in turn, on the phase coexistence and thermodynamics of these mixtures. We study various types of mixtures, ranging from systems of rare gases to biologically and technologically relevant mixtures, such as water-urea and water-carbon dioxide. Comparing the simulation results to the experimental data on mixtures of rare gases allows us to rank the performance of combining rules. We find that the widely used Lorentz-Berthelot rules exhibit the largest deviations from the experimental data, both for the bulk and at coexistence, while the Kong and Waldman-Hagler provide much better alternatives. In particular, in the case of aqueous solutions of urea, we show that the use of the Lorentz-Berthelot rules has a strong impact on the Gibbs free energy of the solute, overshooting the value predicted by the Waldman-Hagler rules by 7%. This result emphasizes the importance of the combining rule for the determination of hydration free energies using molecular simulations.
诸如洛伦兹 - 贝特洛规则之类的组合规则通常用于通过分子模拟来计算混合物的热力学性质。在此，我们扩展了扩展的王 - 兰道模拟方法，以确定组合规则对二元体系配分函数值的影响，进而对这些混合物的相共存和热力学的影响。我们研究了各种类型的混合物，从稀有气体体系到生物和技术相关的混合物，如水 - 尿素和水 - 二氧化碳。将模拟结果与稀有气体混合物的实验数据进行比较，使我们能够对组合规则的性能进行排名。我们发现，广泛使用的洛伦兹 - 贝特洛规则在体相和共存时与实验数据的偏差最大，而孔氏规则和瓦尔德曼 - 哈格勒规则提供了更好的选择。特别是，在尿素水溶液的情况下，我们表明使用洛伦兹 - 贝特洛规则对溶质的吉布斯自由能有很大影响，比瓦尔德曼 - 哈格勒规则预测的值高出7%。这一结果强调了组合规则在使用分子模拟确定水合自由能方面的重要性。
