Optimized Mie Potentials for Phase Equilibria: Application to Branched Alkanes

A transferable
united-atom (UA) force field based on Mie potentials
is presented for branched alkanes. The performance of the optimized
Mie potential parameters is assessed for 32 branched isomers of butane,
pentane, hexane, heptane, and octane using grand canonical histogram-reweighting
Monte Carlo simulations. For each compound, vapor–liquid-coexistence
curves, vapor pressures, heats of vaporization, critical properties,
and normal boiling points are predicted and compared to experiment.
Experimental saturated liquid densities and critical temperatures
are reproduced with a median absolute average error of 0.6%, while
vapor pressures are reproduced with a median absolute average error
of 2.2%. Calculations performed with the TraPPE and NERD force fields
produce median absolute average errors for saturated liquid densities
and vapor pressures of 1.3–1.8% and 14.3–23.5%, respectively.
Binary phase diagrams predicted by the Mie potentials for argon+neopentane,
methane+neopentane, and ethane+isobutane are in close agreement with
experiment.

本研究提出了一种基于米氏势（Mie potentials）的可迁移联合原子（united-atom, UA）力场，适用于支链烷烃的分子模拟。本研究采用巨正则系综直方图重加权蒙特卡洛（grand canonical histogram-reweighting Monte Carlo）模拟方法，针对丁烷、戊烷、己烷、庚烷与辛烷共32种支链异构体，对优化后的米氏势参数性能进行了评估。针对每种化合物，本研究预测了其气液共存曲线、蒸气压、汽化焓、临界性质以及正常沸点，并与实验数据进行了对比。实验饱和液态密度与临界温度的重现性良好，中位数绝对平均误差仅为0.6%；蒸气压的重现性同样优异，中位数绝对平均误差为2.2%。采用TraPPE力场与NERD力场开展的计算，针对饱和液态密度与蒸气压的中位数绝对平均误差分别为1.3%~1.8%与14.3%~23.5%。基于米氏势预测的氩气+新戊烷、甲烷+新戊烷以及乙烷+异丁烷的二元相图，与实验结果吻合度极高。