Development of a fully analytical equation of state using ab initio interaction potentials. Application to pure simple fluids: Noble gases Ne, Ar, Kr, and Xe

In this work, we have extended the first-order mean spherical approximation (FMSA) equation of state (EOS) of Tang and Lu [J. Chem. Phys., 99, 9828 (1993)] in order to predict accurately fluid phase diagrams using ab initio potentials. At this level of development, we restricted to simple spherical compounds. The original equation based on hard-core two-Yukawa (HC2Y) was improved by the following: center dot Adding a new approximate simple correction to include higher orders in the development of Tang and Lu to get an analytical model closer to the full MSA. center dot Including a term to a better account for the long-range behavior of two-body potentials. center dot Adding a three-body interaction term (1(st) order perturbation) based on Axilrod-Teller potential. A general recommendation for setting the hard-sphere diameter value was also given. The predictive capability of the EOS was tested in a systematic manner. First, we checked that various simple theoretical potential (Mie n-6 and Exp n-6) phase diagrams are well reproduced. Second, the EOS was used for predicting fluid phase diagrams of the pure noble gases fluid series Ne, Ar, Kr, and Xe using realistic (i.e. derived from ab initio) two-body and three-body interaction potentials. The model is in good agreement with the experimental phase diagrams. As a conclusion, the simple statistical-mechanics-based fully analytical EOS developed in this work predicts accurately fluid phase diagrams of simple spherical compounds using ab initio potentials. No adjustable parameter was used. This EOS constitutes a strong basis for future development of a predictive model based on ab initio potentials and applicable to more complex compounds.

Automated summary

In this work, the first-order mean spherical approximation equation of state (EOS) was extended to accurately predict fluid phase diagrams using ab initio potentials. The model was tested and found to be in good agreement with experimental phase diagrams, providing a strong basis for future predictive models.