Stokes-Einstein violation for liquids with bounded potentials

The Stokes-Einstein relation between shear viscosity, diffusion constant, and temperature holds in many liquids, but there are certain examples where the relation fails. In this study, we consider liquids where the interaction potential is bounded, and we find that a different behavior of the Stokes-Einstein relation is possible, where the relation between shear viscosity, diffusion constant, and temperature grows linearly with the viscosity. This special behavior occurs when the potential is bounded and full overlap between the particles is possible. We try to show that the peculiar departure from the classical Stokes-Einstein relation can be explained by this possible overlap of particles by using a hydrodynamic model. Then we compare our result with molecular dynamics simulations for the Gaussian core model liquid.