Department of Chemical and Biomolecular Engineering, University of Notre Dame, 182 Fitzpatrick Hall, Notre Dame, Indiana 46556-5637, USA.
J Chem Phys. 2010 Jan 7;132(1):014103. doi: 10.1063/1.3276454.
The reverse nonequilibrium molecular dynamics (RNEMD) method calculates the shear viscosity of a fluid by imposing a nonphysical exchange of momentum and measuring the resulting shear velocity gradient. In this study we investigate the range of momentum flux values over which RNEMD yields usable (linear) velocity gradients. We find that nonlinear velocity profiles result primarily from gradients in fluid temperature and density. The temperature gradient results from conversion of heat into bulk kinetic energy, which is transformed back into heat elsewhere via viscous heating. An expression is derived to predict the temperature profile resulting from a specified momentum flux for a given fluid and simulation cell. Although primarily bounded above, we also describe milder low-flux limitations. RNEMD results for a Lennard-Jones fluid agree with equilibrium molecular dynamics and conventional nonequilibrium molecular dynamics calculations at low shear, but RNEMD underpredicts viscosity relative to conventional NEMD at high shear.
反向非平衡分子动力学（RNEMD）方法通过施加非物理的动量交换并测量由此产生的剪切速度梯度来计算流体的剪切粘度。在本研究中，我们研究了 RNEMD 产生可用（线性）速度梯度的动量通量值范围。我们发现，非线性速度分布主要是由流体温度和密度的梯度引起的。温度梯度是由热量转化为体动能引起的，而动能在其他地方通过粘性加热转化回热量。推导出一个表达式来预测给定流体和模拟单元的指定动量通量产生的温度分布。尽管主要受到限制，但我们也描述了较轻的低通量限制。在低剪切下，Lennard-Jones 流体的 RNEMD 结果与平衡分子动力学和传统非平衡分子动力学计算一致，但在高剪切下，RNEMD 相对于传统 NEMD 预测的粘度较低。
