基于单粒子模型的马尔可夫链蒙特卡罗方法模拟流体混合物的相共存
Phase-coexistence Simulations of Fluid Mixtures by the Markov Chain Monte Carlo Method Using Single-Particle Models
摘要：
我们提出了一个单粒子Lennard-Jones（L-J）模型。其他小的多原子分子的简化的L-J模型可以按照本文描述的方法获得。单组分系统的相共存图计算使用建议的单粒子模型CO2和N2同意在很宽的温度范围内的实验数据。这些图是使用基于Gibbs-NVT系综的马尔可夫链蒙特卡罗（MC）方法计算的。这种良好的协议验证了所提出的简化模型。也就是说，通过适当选择的参数，单粒子模型在预测气相性质方面具有与更复杂的最先进的分子模型相似的精度。为了进一步测试这些单粒子模型，三个二元混合物的CH 4，CO2和N2的研究使用吉布斯-NPT合奏。这些结果进行了比较，在很宽的压力范围内的实验数据。单颗粒模型在气相中具有与传统模型相似的精度，尽管其在液相中的偏差更大。简化模型显著提高了计算效率，特别是在高液体密度的情况下，其中颗粒交换尝试移动的接受率增加。基于Gibbs-NVT系综的MC方法是模拟流体混合物相共存的可行方法。我们比较，在恒定的温度和压力，吉布斯-NPT和吉布斯-NVT合奏，分析他们的性能差异和结果的一致性。正如理论上预测的那样，模拟之间的一致性意味着当实验数据不可用时，Gibbs-NVT可用于验证Gibbs-NPT预测。
英文摘要：
We present a single-particle Lennard-Jones (L-J) model for CO2 and N2. Simplified L-J models for other small polyatomic molecules can be obtained following the methodology described herein. The phase-coexistence diagrams of single-component systems computed using the proposed single-particle models for CO2 and N2 agree well with experimental data over a wide range of temperatures. These diagrams are computed using the Markov Chain Monte Carlo (MC) method based on the Gibbs-NVT ensemble. This good agreement validates the proposed simplified models. That is, with properly selected parameters, the single-particle models have similar accuracy in predicting gas-phase properties as more complex, state-of-the-art molecular models. To further test these single-particle models, three binary mixtures of CH4, CO2 and N2 are studied using a Gibbs-NPT ensemble. These results are compared against experimental data over a wide range of pressures. The single-particle model has similar accuracy in the gas phase as traditional models although its deviation in the liquid phase is greater. The simplified model improves the computational efficiency significantly, particularly in the case of high liquid density where the acceptance rate of the particle-swap trial move increases. The MC method based on Gibbs-NVT ensemble is a viable alternative to simulate phase-coexistence of fluid mixtures. We compare, at constant temperature and pressure, the Gibbs-NPT and Gibbs-NVT ensembles to analyze their performance differences and results consistency. As theoretically predicted, the agreement between the simulations implies that Gibbs-NVT can be used to validate Gibbs-NPT predictions when experimental data is not available.
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