Transport coefficients of simple fluids: Freezing density versus excess entropy scaling

We compare the performance of the freezing density scaling (FDS) and the excess entropy scaling (EES) approaches to the transport properties of simple fluids. Comparison is performed along several isotherms in the Lennard-Jones (LJ) fluid and in the hard-sphere (HS) fluid. Both FDS and EES demonstrate excellent coincidence for each of the reduced coefficients of self-diffusion, shear viscosity, and thermal conductivity along the isotherms considered in the LJ fluid. The level of similarity in the scaling shape of the transport coefficients in the LJ and HS fluids varies with the transport property. For the self-diffusion and viscosity coefficients, the FDS demonstrates a better affinity in the LJ and HS fluids, as compared to the EES. EES demonstrates an almost perfect coincidence of the thermal conductivity coefficients in LJ and HS fluids, while FDS does not. This indicates that there exists no universal mapping between the LJ and HS fluids that would provide an equally good accuracy for all the transport properties simultaneously. Each transport property should be treated separately. We also demonstrate that the EES scaling applies excellently to the product of the self-diffusion and viscosity coefficients in the form of the Stokes-Einstein relation without the hydrodynamic radius. • Freezing density and excess entropy scalings of transport coefficients in dense fluids are examined. • Both scaling demonstrate high accuracy along supercritical isotherms of the Lennard-Jones fluid. • The affinity of scalings in Lennard-Jones and hard-sphere fluids is transport property-dependent. • Stokes-Einstein relation without hydrodynamic radius is consistent with the scalings.