## 3 Results
### Properties
#### 3.2.4 Shear Viscosity  
Viscosities were calculated by the RNEMD method. The systems were divided into 20 slabs in the z axis, and the velocities in the \"x\" direction were swapped between the 1 st and 11 th bins [19; 20; 25]. Velocity profiles were equilibrated for 1 ns. Next, the momentum transferred and velocity gradient were accumulated over 10 ns to ensure the average of the velocity equilibrium. Once the system relaxed, the velocity gradient in the \"x\" direction was almost linear.  
Figure 8: (**a**) Time evolution of the charge flux auto-correlation function (ACF) and the running integral for molten A-6 systems at 900 K. (**b**) The ionic conductivity of six typical systems compared with the pure salts experimental values [36] and Nernst-Einstein equation fitting [33].  
Different swap rates' effect on the linearity of velocity profiles, z direction lengths' effect on the viscosities, and the temperature dependence of velocity profiles were investigated, and the simulation conducted with optimized RNEMD parameters. It was found that momentum swap rates between 20 and 150 time steps showed good linearity velocity gradients, as illustrated in Figure 9a, and 100 was chosen. The larger ones caused a large deviation from the experimental values, as shown in Figure 9b. The z direction box length effect on the results was tested at 900 K. In Figure 10a, all the velocity profile linearity is acceptable (a slightly nonlinear of the velocity gradients will not affect the accuracy of the calculated viscosity values [19]). In Figure 10b, the results showed no obvious change beyond the 2z length in the z direction, and, taking the computation efficiency into account, 2z was picked. The temperature dependence of the velocity gradient was testified, and there is a minor effect of temperature on the linearity of the velocity gradient, as illustrated in Figure 11.  
Figure 10: The influence of the z direction length on A-0 at 900 K. (**a**) Velocity profile of different z lengths. (**b**) The corresponding viscosities (Exp-fit is fitting by the Arrhenius equation based on the data obtained from [37], R\({}^{2}\) = 1.00).  
Figure 9: The swap rate influence on the A-0 at 1200 K. (**a**) Velocity profile of different swap rates. (**b**) The corresponding viscosities (Exp-fit data was obtained from [37].)  
The viscosities obtained from experiments and simulations are plotted in Figure 12. Viscosities calculated by the RNEMD method are in good agreement with the experimental values. The uncertainties of simulated viscosities for A-0, A-2, A-6, and A-8 were under 7%. Since the RNEMD method underestimated viscosities by about 5.8%, 5.2%, and 5.7% for pure molten LiCl, NaCl, and KCl, respectively [26], the simulation results were satisfying. The relatively large discrepancies of A-4 and A-10 (about 20% discrepancy) could be caused by experimental errors, since the A-4 sample corroded the crucible badly and there were slags in the salts during testing. The viscosity monotonously decreased with the increasing temperature.  
Figure 11: Velocity profile of A-0 at different temperatures.  
Figure 12: The experimental and simulated values for A-0, A-2, A-4, A-6, A-8 and A-10 at different temperature(Ref * indexed [37]; Ref ** indexed [38]).