Simulations of the thermodynamic properties of the helium fluid from the state-of-the-art ab initio potentials and their uncertainty estimation

Abstract

ABSTRACT The molecular dynamics simulation method is used to study the internal energy, pressure, isochoric heat capacity, and sound speed of helium based on the state-of-the-art ab initio potentials. The simulations cover a wide temperature and density range of (20–2000) K and (0.0005–70) m o l L − 1 . The uncertainty of simulation data are evaluated based on the uncertainty of the potential and the uncertainty of the simulation method. At temperatures below 300 K, the quantum Feynman-Hibbs modified potential and the Wigner-Kirkwood modified potential are introduced and the results are almost the same as those by the original ab initio potential. The modified potentials can not reasonably describe the quantum effects for the helium fluid at low temperatures, which become obvious below 200 K. The two-body ab initio potential is combined with the three-body ab initio potential to evaluate the influence of multi-body interactions at high densities. When the density is lower than 45 m o l L − 1 , the contribution of the three-body term to our simulation data is not significant. As a result, the three-body potential is omitted in our calculations to improve the overall computational efficiency. The thermodynamic property data of this work show agreement with the experimental data in the literature as well as the NIST Refprop 10.0 data at temperatures above 200 K and densities below 45 m o l L − 1 .