title: Phase separation in hydrogen-helium mixtures at Mbar pressures.
abstract: The properties of hydrogen-helium mixtures at Mbar pressures and intermediate temperatures (4000 to 10000 K) are calculated with first-principles molecular dynamics simulations. We determine the equation of state as a function of density, temperature, and composition and, using thermodynamic integration, we estimate the Gibbs free energy of mixing, thereby determining the temperature, at a given pressure, when helium becomes insoluble in dense metallic hydrogen. These results are directly relevant to models of the interior structure and evolution of Jovian planets. We find that the temperatures for the demixing of helium and hydrogen are sufficiently high to cross the planetary adiabat of Saturn at pressures approximately 5 Mbar; helium is partially miscible throughout a significant portion of the interior of Saturn, and to a lesser extent in Jupiter.
authors.affiliation: Department of Physics, National Center of Supercomputing Applications, and Institute of Condensed Matter Theory, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Morales
authors.forename: Eric
authors.initials: E
authors.lastname: Schwegler
authors.forename: David
authors.initials: D
authors.lastname: Ceperley
authors.forename: Carlo
authors.initials: C
authors.lastname: Pierleoni
authors.forename: Sebastien
authors.initials: S
authors.lastname: Hamel
authors.forename: Kyle
authors.initials: K
authors.lastname: Caspersen