Shear viscosity of ionic liquids from non-equilibrium molecular dynamics simulation

Temperature dependence of viscosity of butyl-3-methylimidazolium hexafluorophosphate is investigated by non-equilibrium molecular dynamics simulations with cosine-modulated force in the temperature range from 360 to 480K. It is shown that this method is able to correctly predict the shear viscosity. The simulation setting and choice of the force field are discussed in detail. The all-atom force field exhibits a bad convergence and the shear viscosity is overestimated, while the simple united atom model predicts the kinetics very well. The results are compared with the equilibrium molecular dynamics simulations. The relationship between the diffusion coefficient and viscosity is examined by means of the hydrodynamic radii calculated from the Stokes-Einstein equation and the solvation properties are discussed.