Pulling simulation predicts mixing free energy for binary mixtures
Pulling simulation predicts mixing free energy for binary mixtures
复制标题
拉动模拟预测二元混合物的混合自由能
DOI：
10.1039/d2sm01065h
复制
发表时间：
2022
期刊：
影响因子：
3.4
通讯作者：
Milner, Scott T.
中科院分区：
文献类型：
--
作者：
Mkandawire, Wezi D.;Milner, Scott T.
利用模拟预测二元混合物的混合自由能是具有挑战性的。提出了一种新的分子动力学（MD）模拟方法，用于提取A和B混合物的化学势μ（X）.物质A和B的每个分子被放置在以模拟箱的中间为中心的相等且相反的谐波势±（1/2）Uex（x）中，导致不均匀的摩尔分数分布X（z），其中A集中在中心，而B集中在外围。结合这些，我们得到Uex（X），所需的交换化学势，以诱导摩尔分数从其平均值的给定偏差。Uex（X）的模拟结果可以拟合到简单的自由能模型，以提取二元混合物的相互作用参数χ。为了说明我们的方法，我们调查苯-吡啶的混合物，这提供了一个很好的例子，经常溶液的行为，使用两个TrapPE联合原子和OPLS全原子势，这两个都已被验证为纯流体性质。用新方法得到的χ值与最近其他模拟方法得到的值一致。然而，TraPPE-UA的结果与从汽液平衡实验数据获得的χ有很大不同，而OPLS-AA的结果与实验合理一致，突出了准确的势在正确表示混合物行为中的重要性。
Predicting the mixing free energy of mixing for binary mixtures using simulations is challenging. We present a novel molecular dynamics (MD) simulation method to extract the chemical potential μ(X) for mixtures of species A and B. Each molecule of species A and B is placed in equal and opposite harmonic potentials ±(1/2)Uex(x) centered at the middle of the simulation box, resulting in a nonuniform mole fraction profile X(z) in which A is concentrated at the center, and B at the periphery. Combining these, we obtain Uex(X), the exchange chemical potential required to induce a given deviation of the mole fraction from its average. Simulation results for Uex(X) can be fitted to simple free energy models to extract the interaction parameter χ for binary mixtures. To illustrate our method, we investigate benzene–pyridine mixtures, which provide a good example of regular solution behavior, using both TraPPE united-atom and OPLS all-atom potentials, both of which have been validated for pure fluid properties. χ values obtained with the new method are consistent with values from other recent simulation methods. However, the TraPPE-UA results differ substantially from the χ obtained from VLE experimental data, while the OPLS-AA results are in reasonable agreement with experiment, highlighting the importance of accurate potentials in correctly representing mixture behavior.