Department of Chemical Engineering, Brigham Young University, Provo, Utah 84602, USA.
J Chem Phys. 2011 Jan 14;134(2):024526. doi: 10.1063/1.3543798.
A transient molecular dynamics (TMD) method for obtaining fluid viscosity is extended to multisite, force-field models of both nonpolar and polar liquids. The method overlays a sinusoidal velocity profile over the peculiar particle velocities and then records the transient decay of the velocity profile. The viscosity is obtained by regression of the solution of the momentum equation with an appropriate constitutive equation and initial and boundary conditions corresponding to those used in the simulation. The transient velocity decays observed appeared to include both relaxation and retardation effects. The Jeffreys viscoelastic model was found to model accurately the transient responses obtained for multisite models for n-butane, isobutane, n-hexane, water, methanol, and 1-hexanol. TMD viscosities obtained for saturated liquids over a wide range of densities agreed well for the polar fluids, both with nonequilibrium molecular dynamics (NEMD) results using the same force-field models and with correlations based on experimental data. Viscosities obtained for the nonpolar fluids agreed well with the experimental and NEMD results at low to moderate densities, but underpredicted experimental values at higher densities where shear-thinning effects and viscous heating may impact the TMD simulations.
一种用于获取流体粘度的瞬态分子动力学（TMD）方法被扩展到非极性和极性液体的多站点力场模型。该方法在特殊粒子速度上叠加正弦速度分布，然后记录速度分布的瞬态衰减。通过将动量方程的解与适当的本构方程回归，并使用与模拟中相同的初始和边界条件来获得粘度。观察到的瞬态速度衰减似乎包括弛豫和滞后效应。杰弗里斯粘弹性模型被发现可以准确地模拟多站点模型对正丁烷、异丁烷、正己烷、水、甲醇和 1-己醇的瞬态响应。在很宽的密度范围内，对饱和液体进行的 TMD 粘度与使用相同力场模型的非平衡分子动力学（NEMD）结果以及基于实验数据的相关性都很好地吻合，对于极性液体。对于非极性液体，在低到中等密度下，与实验和 NEMD 结果吻合较好，但在较高密度下，剪切变薄效应和粘性加热可能会影响 TMD 模拟，从而导致预测值低于实验值。
