Limitations and recommendations for the calculation of shear viscosity using reverse nonequilibrium molecular dynamics.
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.
Tenney
Craig M
CM
Department of Chemical and Biomolecular Engineering, University of Notre Dame, 182 Fitzpatrick Hall, Notre Dame, Indiana 46556-5637, USA.
Maginn
Edward J
EJ