Further investigation on the validity of Stokes-Einstein behaviour at the molecular level

Stokes–Einstein behaviour at the molecular level is investigated by simulating water at different temperatures and by simulating `water' models with different mass distributions. When combining Stokes' law for the viscosity with Einstein's formula for the diffusivity, an expression for the product of these quantities is obtained, which shows that the product of diffusivity and viscosity should be independent of the mass distribution and positively proportional to the temperature. Using both, equilibrium and non-equilibrium simulation techniques to compute the viscosity slight deviation from Stokes–Einstein behaviour was found for the `water' models and temperatures investigated. Non-equilibrium simulation seems to yield systematically lower values for the viscosity than the equilibrium simulation.