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Evaluation of Viscosity by Using MD
Viscosity can be evaluated by calculating the shear deformation using LeesEdwards boundary conditions.
Results for ndecane and nhexadecane are shown below. Using the full atomistic model created with JOCTA, the calculations were carried out with a density of 0.613 g/cm3 and a temperature of 480 K for ndecane and a density of 0.753 g/cm3 and a temperature of 323 K for nhexadecane. The numbers of molecules in the system for the two substances were respectively 200 and 100. The viscosity was evaluated while varying the shear rate from 1e+12 [1/s] to 1e+10 [1/s]. VSOP was used for the MD calculations (Fig. 1).
Fig. 2 shows a double logarithmic plot of the calculated viscosity versus the shear rate. It can be seen that the viscosity increases with decreasing shear rate; however, for ndecane, the viscosity approaches a constant value when the shear rate is at 1e+10 [1/s] or below.
In the viscosity evaluation using the GreenKubo method in Reference [1], the viscosity of ndecane under similar conditions is 0.178 [e3 Pa·s] and the viscosity of nhexadecane is 1.17 [e3 Pa·s].
Fig. 1. Simulation system with the LeesEdwards boundary condition.
Fig. 2. Evaluated viscosity.
 Reference
 [1] S. T. Cui, P. T. CUMMINGS and H. D. COCHRAN, Molecular Physics, 1998, 93, 1, 117121