Kikugawa et al. realized, that for orthorhombic box geometries, the presence of unequal box lengths will lead to different system size dependencies for each of the components D ii of the diffusion tensor D, such that the self-diffusion tensor will become anisotropic even for an isotropic fluid. To describe this behavior, they followed the strategy of Yeh and Hummer and applied the Ewald technique to Equation , and derived expressions for systems with an orthorhombic geometry, leading to