where D 0 denotes the true scalar diffusion coefficient within an infinite system. To transform equation 5 into something, which could be computed numerically, the technique of Ewald summation was used, as suggested earlier by Hasimoto and Beenakker. The result is a model, describing the system size dependence of self-diffusion coefficients from MD simulations with PBCs, based on the effect of hydrodynamic interactions between particles in a periodic system.