Size Effect on Transport Properties of Liquid Argon: A Molecular Dynamics Simulation Study

Abstract

In a recent study, we have examined the Green-Kubo formula for the calculation of transport properties (diffusion coefficient, viscosity, and thermal conductivity) of noble gases (He, Ne, Ar, Kr, and Xe) by carrying out a series of equilibrium molecular dynamics (EMD) simulations for the system of N=1728 at 273.15 K and 1.00 atm. 1 While the diffusion coefficients (D) of noble gases were obtained through the original Green-Kubo formula, the viscosities (η) and thermal conductivities (λ) were obtained by utilizing the revised Green-Kubo formulas. 2,3 The structural and dynamic properties of gaseous argon are completely different from those of liquid argon at 94.4 K and 1.374 g/cm 3 . The results for transport properties (D, η, and λ) at 273.15 K and 1.00 atm obtained from our EMD simulations are in general agreement with the experimental data and superior to the rigorous results of the kinetic theory. 4 The error estimates, (XMD-XExp)/XExp, were reported as −0.6, −21.4, and −12.3% for X = D, η, and λ of gaseous argon for the system of N = 1728 at 273.15 K and 1.00 atm, respectively. 1 While the agreement between the MD results and the experimental measure for D is excellent, those for η and λ are acceptable but rather unsatisfied. In this note, we perform EMD simulations for gaseous argon of the systems of N = 432, 1728, and 6912 at 273.15 K and 1.00 atm. The primary goal of this study is to examine the size effect on the transport properties (D, η, and λ) of gaseous argon. Green-Kubo Formula and Molecular Dynamics Simulation. The diffusion coefficient is obtained through two routes: the Green-Kubo formula from velocity auto-correlation (VAC) function: