Limits of classical molecular simulation on the estimation of thermodynamic properties of cryogenic hydrogen

In this study, we investigated the limits of classical molecular simulation on the estimation of thermodynamic properties of cryogenic hydrogen. Three empirical potentials, the Lennard-Jones (LJ) potential, two-centre LJ (2CLJ) potential, and modified Buckingham (exp-6) potential and an ab initio potential model derived by the molecular orbital calculation were applied. Molecular dynamics (MD) simulations were performed across a wide density-temperature range. Using these data, the equation of state (EOS) was obtained by Kataoka's method, and they were compared with National Institute of Standards and Technology (NIST) data using the principle of corresponding states. As a result, it was confirmed that the potential model has a large effect on the estimated thermodynamic properties of cryogenic hydrogen. On the other hand, from the viewpoint of the principle of corresponding states, we obtained the same results from the empirical potential models as from the ab initio potential showing that the potential model has only a small effect on the reduced EOS: the classical MD results could not reproduce the NIST data in the high-density region. This difference is thought to arise from the quantum effect in actual liquid hydrogen.