[42] We want to point out that Vögele and Hummer have derived a similar approach using Beenakker's expression for the Rotne-Prager tensor under PBCs. Note that Equations 6 and 7 are based on solving the linearized Navier-Stokes equation for an incompressible fluid. D.M. Heyes and co-workers have shown that for compressible fluids at low densities, the finite-size effects of self-diffusivities scale differently with the system size, and the related scaling exponent varies according to the packing fraction of the fluid. From a numerical evaluation of Equation 7 follows that for a cubic unit cell the computed Madelung constant analogues are all identical, with ζ ii ≈ 2.8372974795. Consequently, the obtained self-diffusion coefficients D PBC,ii are always smaller than the true self-diffusion coefficient D 0 . For orthorhombic unit cells with L x = L y = L z , however, diffusion in xand y-direction can even become accelerated. Based on Equation 7, the exact ratio where this happens has been obtained by computing the Madelung constant analogues ζ xx , ζ yy , and ζ zz . In accordance with the analysis of Kikugawa et al. , the condition ζ xx = ζ yy = 0 was found be related to a box geometry with a "magic" box length ratio of L z /L x = L z /L y ≈ 2.7933596497. For this geometry, the Madelung constant analogue in z-direction was determined to be ζ zz ≈ 8.1711245653. Since we have two unknowns, D 0 and η, and three equations, it will always be possible to determine both quantities from the direction-dependent diffusion coefficients obtained from an MD simulation of an orthorhombic system. We have explored this approach recently for MD simulations of TIP4P/2005 water, testing a variety of different box geometries. However, the use of an orthorhombic box with L z /L x = L z /L y ≈ 2.7933596497 has been shown to be more efficient, and is also more appealing, since the xand ycomponents of the diffusion tensor become system size independent such that D PBC,xx = D PBC,yy = D 0 , and the selfdiffusion coefficient for an infinitely large system can be simply obtained as their arithmetic mean