The research team proposes a sequence of quantum Monte Carlo simulations of dense hydrogen and helium to understand their respective phase diagrams and make predictions that can be verified in laboratory experiments. Dense hydrogen and helium make up most of the mass of giant planets, so knowledge of their properties are essential for understanding but the conditions of temperature and pressure are not easily accessible experimentally. Hydrogen exhibits a rich phase diagram, but even rough estimates of the sequence of phase and their conditions is only now becoming known.
We have developed an accurate quantum Monte Carlo approach to simulate electron-ion systems starting from the bare Colomb interaction and able to make such simulations at a wide range of thermodynamics conditions. There has been sufficient computational and algorithmic progress such that errors can be controlled and truly ab initio predictions made. However, recent studies of the deuterium Hugoniot and the liquid-liquid transition in hydrogen and deuterium show significant discrepancies with respect to shock experiments conducted at Sandia and Lawrence Livermore national laboratories. It is important that such differences be resolved. The team plans new calculations to study these phenomena in dense liquid helium.
We use the Coupled-Electron-Ion Monte Carlo method as implemented in the codes BOPIMC and QMCPACK. The method employs several different parallelization strategies and is able to scale to many nodes efficiently. The QMCPACK software uses the GPUs on Titan efficiently, outperforming the CPU code by a factor of 4.5.
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