### Ab-initio simulations of hydrogen and helium at high pressure using Quantum Monte Carlo

#####
** Miguel Morales,
University of Illinois, Urbana-Champaign **

We study the properties of hydrogen, helium and their mixtures at Mbar pressures and intermediate temperatures (2000K-10000K) using the Coupled Electron-Ion Monte Carlo (CEIMC) method. The CEIMC method is based on the Born-Oppenheimer approximation and consists on a Monte Carlo simulation of the ionic degrees of freedom (using either path integrals or classical Metropolis) using the potential energy surface obtained from a zero temperature Quantum Monte Carlo (QMC) calculation. By solving the electronic problem with QMC we can go beyond the usual single-body approximations, like Density Functional Theory, and obtain results with a very high accuracy. The main goal of our research is to obtain an accurate description of the high pressure phase diagram of the hydrogen-helium system, where many complicated physical processes occur, like molecular dissociation, metalization and immiscibility. We present some preliminary results including the equation of state and structural properties of hydrogen in the dissociation and metallic regime and the equation of state of the mixture as a function of composition.

**Abstract Author(s):** Miguel A. Morales, Carlo Pierleoni, Kris Delaney, David Ceperley and Markus Holzmann