The viscosity simulations were performed using a smaller box, containing 100 PAO4 molecules, since previous MD studies have demonstrated a weak system size-dependence using the Green-Kubo method. Periodic boundary conditions were applied in all directions and the systems underwent the same equilibration procedure as described for the thermal conductivity calculations. The equilibrated systems then ran in the NVT ensemble for 50 ns, during which time the integral of the PACF was calculated to obtain the viscosity, using equation 5. The viscosity was obtained by calculating the mean of the viscosity profile once it had converged. The autocorrelation was calculated with a sample rate, s, of 10 fs, correlation length, p, of 100,000 fs over a correlation time period, d = sp = 1000 ps. For an explanation of how the correlation time, d, was determined, see the Supplementary Information.