A well-established interaction potential, the Optimized Potential for Liquid Simulation All-Atom (OPLS-AA) force-field, within the MD framework was used to determine self- and mutual diffusivity of several near-critical and supercritical fluids. The test fluids were benzene, heptane and carbon dioxide. The Green-Kubo method yielded considerably overestimated values of self-diffusivity; better results were obtained with use of Stokes-Einstein method. In addition, a number of relatively significant problems with the default OPLS-AA parameterization were identified. There exist ranges of pressure and temperatures, where the results for the selected pure fluids show good agreement with experiment, and thus reparameterization of OPLS-AA may not be required. However, the results for mixtures all show significant deviation from experiment. Based on the observed results, the current predictive power of OPLS-AA for mass diffusivity of supercritical fluids is not satisfactory. We are therefore convinced that a systematic reparameterization of OPLS-AA both in terms of the intermolecular (van der Waals, electrostatic) and intramolecular (bonding) interactions is needed to increase its accuracy.
Citation: Technical Note (NIST TN) - 1805
NIST Pub Series: Technical Note (NIST TN)
Pub Type: NIST Pubs
mass diffusion, molecular dynamics