Using the Zeno line to assess and refine molecular models

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Paterson, Thomas and Bannerman, Marcus N. and Lue, Leo (2024) Using the Zeno line to assess and refine molecular models. Journal of Chemical Physics, 160 (15). 154503. ISSN 0021-9606 (https://doi.org/10.1063/5.0192770)

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Abstract

The Zeno line is the locus of points on the temperature-density plane where the compressibility factor of the fluid is equal to one. It has been observed to be straight for a broad variety of real fluids, although the underlying reasons for this are still unclear. In this work, a detailed study of the Zeno line and its relation to the vapor-liquid coexistence curve is performed for two simple model pair-potential fluids: attractive square-well fluids with varying well-widths λ, and Mie n-6 fluids with different repulsive exponents n. Interestingly, the Zeno lines of these fluids are curved, regardless of the value of λ or n. We find that for square-well fluids, λ ≈ 1:8 presents a Zeno line which is the most linear over the largest temperature range. For Mie n-6 fluids, we find that the straightest Zeno line occurs for n between 8 and 10. Additionally, the square-well and Mie fluids with the straightest Zeno line showed the closest quantitative agreement with the vapor-liquid coexistence curve for experimental fluids that follow the principle of corresponding states (e.g., argon, xenon, krypton, methane, nitrogen, and oxygen). These results suggest that the Zeno line can provide a useful additional feature, in complement to other properties such as the phase envelope, to evaluate molecular models.

ORCID iDs

Paterson, Thomas, Bannerman, Marcus N. and Lue, Leo ORCID logoORCID: https://orcid.org/0000-0002-4826-5337;
CORE (COnnecting REpositories)