Shear Viscosities of Sodium and Nickel from NEMD Simulations


T. Cagin, K.A. Mansour, W.A. Goddard

Abstract

Shear viscosities of liquid sodium and liquid nickel are determined using nonequilibrium molecular dynamics (NEMD) simulations. The interactions between sodium ions are represented using a density-dependent potential derived using second order perturbation theory with an empty core local pseudopotential. Using a 432 atom system and the experimental density at each temperature we calculated the viscosity at a number of shear rates. The NEMD results for sodium are in better agreement with the experiment than earlier Green-Kubo calcualtions using the same potential. The interactions between Nickel atoms are represented by a many-body potential using form due to Sutton and Chen, parameters of the potentials are modified to accurately represent phonon spectra and vacancy and surface formation energies. Using a 500 atom system and the experimental density at each temperature we calculated the viscosity at a number of shear rates for nickel (T_m = 1726K) at temperature up to 3000K. The predicted visosity are in good agreement with experiment.

Shear Viscosity of Liquid Gold, Copper, and Gold-Copper Alloy

Y. Qi, T. Cagin, K. A. Mansour, Y. Kimura, W. A. Goddard

Abstract

Using NEMD method we have calculated the shear viscosities of Au, Cu and Au-Cu alloys at elevated temperatures. The interactions for Cu, Au and Au-Cu alloy are represented by a many-body potential form due to Sutton and Chen, but the parameters for the potentials are modified to accurately represent phonon spectra and vacancy and surface formation energies [Kimura, Cagin and Goddard]. Using 500 atom model systems and the experimental density at each temperature we calculated the viscosity at a number of shear rates for the model systems at temperatures up to 3000K. The predicted viscosity are in good agreement with experiment. Copper-Gold alloy simulations are carried out at three different concentrations , 25%, 50% and 75%. recently developed many body potentials [Kimura, Cagin, Goddard] for FCC metals we have calculated the shear viscosities of Au, Cu and Au-Cu alloys at elevated temperatures.