Table II summarizes the results from MD simulations of TIP4P/2005 water using orthorhombic unit cells with L z /L x = L z /L y ≈ 2.7933596497 for system sizes between 768 and 6144 water molecules. The diffusion coefficients D 0 obtained from the simulations extending over 40 ns with n W = 80 given in Table II seem to suggest a slight system size dependence: in particular for the system containing 768 molecules, the value obtained for D 0 is found to be slightly smaller, and the value for η is slightly larger, when compared with the three larger systems. The data for the simulations of the 768 water molecules extending over 160 ns with n W = 320, however, show that this effect is just a statistical aberration. When computing the data for D 0 and η from the prolonged simulations, as shown in Figure , we find them in perfect agreement with the data computed for the systems with N W > 768 and n W = 80. The selfdiffusion coefficient averaged over all system sizes is D 0 = (2.2994 ± 0.0053) × 10 -9 m 2 s -1 . Here we have included the value for n W = 320 for the 768 molecule system. As indicated in Figure , the computed self-diffusion coefficients in z-direction D PBC,zz show the expected strong system size dependence. The size of the relative error for D 0 obtained from individual simulation runs ranges from 0.4 % to 0.8 %, while the errors for D PBC,zz are smaller, and vary between 0.2 % to 0.4 %. From the knowledge of D 0 and D PBC,zz we compute the shear viscosity η. The computed viscosities for all systems are shown in Table . The average viscosity for TIP4P/2005 water at T = 298 K is η = (0.860 ± 0.018) mPa s, when averaging over all systems, and using the value for n W = 320 for the 768 molecule system. In Figure , we plot the difference D 0 -D PBC,zz vs. L -1 z , as suggested by equation 9. A linear fit of the data, shown as red solid line, yields an intercept value of 0.0092 × 10 -9 m 2 s -1 , which is about of the size of the uncertainties for D 0 given in Table . The corresponding slope of 2.0055 × 10 -18 m 3 s -1 yields a viscosity of 0.889 mPa s. If the data-point (0,0) is included in the fit, the resulting slope of 2.0588 × 10 -18 m 3 s -1 leads to 0.866 mPa s. If the intercept at (0,0) is enforced, and a viscosity of 0.861 mPa s is obtained. The two latter values for the viscosity agree perfectly well with the computed weighted average of η = (0.860 ± 0.018) mPa s.