Accurate calculation of near-critical heat capacities CP and CV of argon using molecular dynamics.

Abstract

Molecular dynamics (MD) employing the Lennard-Jones (LJ) interaction potentialwas used to compute the heat capacities of argon at constant volume CV and constant pressure CP near the critical point very close to the asymptotic region. The accurateMD calculation of critical divergenceswas shown to be related to a careful choice of the cutoff radius rc and the inclusion of long-range corrections in the LJ potential. The computed CP and CV values have very good agreement as compared to available NIST data. Furthermore, values of CV in a range of temperatures for which NIST data is not available could be computed. In the investigated range of temperatures, both CP and CVMD results were fitted to a simple mathematical expression based on an empirical model that describes the critical effectswhen the asymptotic models are not appropriate. The present approach is of general applicability and robust to compute thermophysical properties of fluids in the near-critical region.