Ionization and transport in partially ionized multicomponent plasmas: Application to atmospheres of hot Jupiters.

We study ionization and transport processes in partially ionized multicomponent plasmas. The plasma composition is calculated via a system of coupled mass-action laws. The electronic transport properties are determined by the electron-ion and electron-neutral transport cross sections. The influence of electron-electron scattering is considered via a correction factor to the electron-ion contribution. Based on these data, the electrical and thermal conductivities as well as the Lorenz number are calculated. For the thermal conductivity, we consider also the contributions of the translational motion of neutral particles and of the dissociation, ionization, and recombination reactions. We apply our approach to a partially ionized plasma composed of hydrogen, helium, and a small fraction of metals (Li, Na, Ca, Fe, K, Rb, and Cs) as typical for atmospheres of hot Jupiters. We present results for the plasma composition and the transport properties as a function of density and temperature and then along typical P-T profiles for the outer part of the hot Jupiter HD 209458b. The electrical conductivity profile allows revising the Ohmic heating power related to the fierce winds in the planet's atmosphere. We show that the higher temperatures suggested by recent interior models could boost the conductivity and thus the Ohmic heating power to values large enough to explain the observed inflation of HD 209458b.

Gibbs-ensemble Monte Carlo simulation of H_{2}-He mixtures.

We explore the performance of the Gibbs-ensemble Monte Carlo simulation technique by calculating the miscibility gap of H_{2}-He mixtures with analytical exponential-six potentials. We calculate several demixing curves for pressures up to 500 kbar and for temperatures up to 1800K and predict a H_{2}-He miscibility diagram for the solar He abundance for temperatures up to 1500K and determine the demixing region. Our results are in good agreement with ab initio simulations in the nondissociated region of the phase diagram. However, the particle number necessary to converge the Gibbs-ensemble Monte Carlo method is yet too large to offer a feasible combination with ab initio electronic structure calculation techniques, which would be necessary at conditions where dissociation or ionization occurs.

Ab Initio Calculation of the Miscibility Diagram for Hydrogen-Helium Mixtures.

We use finite-temperature density functional theory coupled to classical molecular dynamics simulation to calculate the miscibility gap of hydrogen-helium mixtures. The van der Waals density functional (vdW-DF) theory is used, which leads to lower demixing temperatures compared to computations using the Perdew-Burke-Ernzerhof functional. Our calculations suggest that current Jupiter models are most likely too hot to allow demixing in the interior. A Jupiter isentrope based on our vdW-DF data is presented. Our demixing phase diagram still predicts phase separation in Saturn, but in a significantly reduced fraction of its volume.

Free energy model for solid high-pressure phases of carbon.

Analytic free energy models for three solid high-pressure phases--diamond, body centered cubic phase with eight atoms in the unit cell (BC8), and simple cubic (SC)--are developed using density functional theory. We explicitly include anharmonic effects by performing molecular dynamics simulations and investigate their density and temperature dependence in detail. Anharmonicity in the nuclear motion shifts the phase transitions significantly compared to the harmonic approximation. Furthermore, we apply a thermodynamically constrained correction that brings the equation of state in accordance with diamond anvil cell experiments. The performance of our thermodynamic functions is validated against Hugoniot experiments.