Structure and energetics of fluid para-hydrogen

The properties of neat fluid para-hydrogen from the low temperature liquid to the subcritical fluid (T = 14–25 K) are studied in the isothermal–isobaric ensemble using the Path Integral Monte Carlo method. The molecules are treated as spheres and are assumed to interact via a pair potential. This is a good approximation at low pressures as the anisotropic part of the potential surface is very small and the molecules are in J = 0 at the temperatures of interest. The volume and energy of the system are determined as a function of temperature and good agreement is found with experiment. In addition, radial distribution functions and structure factors are calculated for the molecular centers of mass. The extreme quantum nature of the system is illustrated by comparisons to the corresponding classical model of the system.