Nonequilibrium molecular dynamics simulation of shear viscosity of polar liquids

Nonequilibrium molecular dynamics (NEMD) simulations were performed on model polar fluids representing acetone, propyl chloride, formamide, and dimethyl formamide. The purposes of the study were (1) to test further a recently developed method for applying the Ewald sum treatment of long-range forces to NEMD simulations with Lees-Edwards boundary conditions, (2) to study the effect of different constituent groups and their partial charges upon fluid viscosity, and (3) to examine the relative magnitudes of the van der Waals and coulombic contributions to fluid viscosity. The new Ewald sum method worked well, producing simulated viscosities for all four fluids that were in good agreement with correlated experimental data. Generally, viscosities predicted without the partial charges were significantly low and exhibited an incorrect density dependence. While methyl chloride's viscosity is due primarily to the dispersion interactions, coulombic interactions contribute substantially to the viscosity of the other three fluids, particularly at higher densities.