Entropy scaling laws for diffusion.

2 /8ρσ the Enskog and Boltzmann diffusion coefficients [3], χ the contact value of the pair correlation function, se the excess entropy per particle, and A = 2.5. Using the excess entropy se/kB = −(4η − 3η )/(1 − η) and contact value χ = (2 − η)/2(1 − η) given by the Carnahan-Starling equation of state [4] (η = πρσ/6 packing fraction), we test this relation against the molecular dynamics simulation results of Erpenbeck and Wood (EW)[5] Fig. 1. The disagreement is quite significant and more important the behavior of the two curves is very different, as (D/DE)EW is not a monotonically decreasing function of (−se/kB). The discrepancy cannot be attributed to the authors use of an approximation for the excess entropy. The idea of entropy scaling for transport coefficients has a fairly long history [6]. Arguing on the basis of the molecular “caging” effect Dzugutov [2] proposed the scaling law: