  In this Research Note the Zwanzig's formulation of the Stokes-Einstein (SE)
relation for simple atomistic fluids is re-examined. It is shown that the value
of the coefficient in SE relation depends on the ratio of the transverse and
longitudinal sound velocities. In some cases, this ratio can be directly
related to the pair interaction potential operating in fluids and thus there
can be a certain level of predictivity regarding the value of this coefficient.
This Research Note provides some evidence in favour of this observation. In
particular, analyzing the situation in several model systems such as
one-component plasma, Yukawa, inverse-power-law, Lennard-Jones, and hard-sphere
fluids, it is demonstrated that there are certain correlations between the
interaction softness and the coefficient in SE relation. The SE coefficient is
also re-evaluated for various liquid metals at the melting temperature, for
which necessary data are available.
