优化温度相关力场预测正构烷烃热力学性质

为了实现不同温度下正构烷烃及其混合物热力学性质的准确预测，以正构烷烃（n-C₄~C₁₀）为训练集，通过对全原子OPLS-AA力场中非键相互作用参数（ε）的模拟优化，得到了ε与对比温度（T_r）以及正构烷烃碳原子个数（N_C）的经验关系式。利用该关系式计算出不同温度不同种类的正构烷烃的ε值，预测了正构烷烃纯物质及其混合物的黏度、密度、扩散系数等物性，并将新力场模拟计算值与理论估算值以及实验值进行比较。结果表明，采用优化温度相关力场预测烷烃及其混合物的物性与实验值最为吻合。密度、黏度和扩散系数的预测值与实验值的相对偏差分别小于2%、5%和10%，显著优于目前的理论方法和原OPLS-AA力场模拟计算的预测值。上述温度相关力场参数的确立，对于利用分子动力学模拟方法准确地预测正构烷烃及其混合物的热力学性质具有重要的实际应用价值。

Prediction of thermodynamic properties of n-alkanes based on temperature-corrected force field

Aim to accurately predict the thermodynamic properties of n-alkanes and their mixtures at different temperature, in this paper, the non-bond Lennard-Jones (L-J) interaction parameter, ε, was optimized by using n-C₄-C₁₀ as the training set and all-atom molecular dynamics simulations. Here an empirical relationship between the L-J parameter (ε) and the reduced temperature (T_r) and carbon atomic number of n-alkanes (N_C) was obtained. According to above-mentioned relationship, the values of ε at different temperatures were successfully calculated. Further, the properties of viscosity, density and diffusion coefficient of different n-alkanes and their mixtures were predicted using traditional and non-equilibrium molecular dynamics simulations with all-atom OPLS-AA force field corrected by temperature-dependent ε. Compared with previous theoretical prediction values and experimental data, the prediction with temperature-dependent ε showed that the physical properties of n-alkanes and their mixtures predicted by this method were in the best agreement with the experimental values. The relative deviations between the predicted values of density, viscosity and diffusion coefficient and their corresponding experimental counterparts were less than 2%, 5% and 10%, respectively. The new predicted values are significantly superior to those predicted by both other theoretical methods and molecular dynamics simulations with the original OPLS-AA force field. Therefore, the established temperature-dependent force field has important practical application value for accurately predicting the thermodynamic properties of n-alkanes and their mixtures by molecular dynamics simulations.