Diffusion and viscosity coefficient in Lennard-Jones fluids: excess entropy scaling law

Abstract

We investigated the proportional relationship between the diffusion coefficient and the viscosity coefficient and excess entropy in Lennard-Jones fluids. Based on the theoretical basis of Dzugutov and Bell et al., we came up with a new expression. Using molecular dynamics simulation to calculate the radial distribution function (RDF), the reduced diffusion coefficient D* and the reduced shear viscosity coefficient η* in the state of reduced density ρ* = 0.5 and the reduced temperature range of 1 ≤ T* ≤ 2.8. The two body excess entropy S2 was calculated from RDF. The results showed that the reduced diffusion coefficient and the reduced viscosity coefficient and the excess entropy present the exponential scaling behaviour. Our results supported the notion put forth by Dzugutov and Bell et al. but had different adjust parameters. The dependence of the reduced diffusion coefficient on the reduced temperature are also explored, they qualitatively exhibited a 2/3 power function relationship. In addition, we have quantitatively calculated the relation schema of ln(η*)-ln(D*/T*) in Lennard-Jones fluids that with LJ potential (n = 12) without considering the influence of the packing fraction and found that the reduced diffusion coefficient and reduced viscosity satisfy the new Stokes–Einstein relationship proposed by Ohtori et al.