title: Equation of state of metallic hydrogen from coupled electron-ion Monte Carlo simulations.
abstract: We present a study of hydrogen at pressures higher than molecular dissociation using the coupled electron-ion Monte Carlo method. These calculations use the accurate reptation quantum Monte Carlo method to estimate the electronic energy and pressure while doing a Monte Carlo simulation of the protons. In addition to presenting simulation results for the equation of state over a large region of the phase diagram, we report the free energy obtained by thermodynamic integration. We find very good agreement with density-functional theory based molecular-dynamics calculations for pressures beyond 600 GPa and densities above rho=1.4 g/cm(3) , both for thermodynamic and structural properties. This agreement provides a strong support to the different approximations employed in the density-functional treatment of the system, specifically the approximate exchange-correlation potential and the use of pseudopotentials for the range of densities considered. We find disagreement with chemical models, which suggests that a reinvestigation of planetary models--previously constructed using the Saumon-Chabrier-Van Horn equations of state--might be needed.
authors.affiliation: Department of Physics, University of Illinois at Urbana-Champaign, Illinois 61801, USA. mmorale3@illinois.edu
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Morales
authors.forename: Carlo
authors.initials: C
authors.lastname: Pierleoni
authors.forename: D M
authors.initials: DM
authors.lastname: Ceperley