New equation of state and force fields for hydrogen, helium, neon and deuterium

Our article entitled Equation of state and force fields for Feynman–Hibbs-corrected Mie fluids. I. Application to pure helium, neon, hydrogen, and deuterium has just been published in the Journal of Chemical Physics.

Liquefaction of hydrogen is a promising method for large-scale transport and distribution of hydrogen across long distances. Mixtures between helium-hydrogen and neon may have the potential to significantly improve the energy efficiency of the hydrogen liquefaction process when used as refrigerant. These fluids can be liquids at temperatures below 50~K. However, at sufficiently low temperatures, they exhibit strong quantum effects, in particular helium. Because of these quantum effects, there is currently no accurate equation of state available for mixtures between helium, neon and hydrogen.

One way to emulate the influence of the wave-particle duality on classical interaction potentials is by using Feynman-Hibbs corrections. In the paper above, we use Mie potentials to represent the classical part of the interaction potential and investigate to which extent Mie-Fluids with first and second order Feynman-Hibbs correction can represent the thermodynamic properties of hydrogen, helium, neon and deuterium. The good thing with these quantum corrections is that they introduce no new fitting parameters in comparison to classical Mie fluids. We find that the quantum corrections improve significantly the accuracy for all fluids, where a comparison between the force field/interaction potential, the perturbation theory/EoS and the most accurate equation of state available for hydrogen (solid line) is shown below. The figure displays excellent agreement between the equation of state, the underlying potential and the properties of hydrogen and a vast improvement in comparison to the cubic equation of state, SRK. We are currently working to finalize force fields for mixtures between these fluids as well.

This work has indeed been a team effort and would not have been possible without the excellent contributions from Ailo Aasen, Morten Hammer, Åsmund Ervik and Erich A. Müller from Imperial Collegue in London.

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