THERMODYNAMIC PROPERTIES AND PHASE-EQUILIBRIUM OF FLUID HYDROGEN FROMPATH-INTEGRAL SIMULATIONS

The thermodynamic properties of normal and para-hydrogen are computed from multiple time-step path integral hybrid Monte Carlo (PIHMC) simul ations. Four different isotropic pair potentials are evaluated by comp aring simulation results with experimental data. The Silvera-Goldman p otential is found to be the most accurate of the potentials tested for computing the density and internal energy of fluid hydrogen. Using th e Silvera-Goldman potential, simulation and experimental data are comp ared on isobars ranging from 0.1 to 100 MPa and for temperatures from 18 to 300 K. The Gibbs free energy is calculated from the PIHMC simula tions by an adaptation of Widom's particle insertion technique to a pa th integral fluid. A new method is developed for computing phase equil ibria for quantum fluids directly by combining PIHMC with the Gibbs en semble technique. This Gibbs-PIHMC method is used to calculate the vap our-liquid phase diagram of hydrogen from simulations. Agreement with experimental data is good.