Equation of State and Phase Diagram of Magnesium Oxide from First-Principle Simulations

Accurate equations of state (EOS) and phase diagrams for silicate materials are key to understand the interiors of Earth, Super-Earths and the cores of giant planets. While recent shock wave experiments have provided new data on the principal Hugoniot curve, accessing off-Hugoniot states is much more challenging. Ab initio computer simulations offer the possibility to complement the experiments in this regard. Here we report results of an extensive set of ab initio simulations of MgO in solid B1 and B2 and liquid phases over a wide range of parameters relevant for planetary interiors. Using molecular dynamics methods in combination with a thermodynamic integration technique, we derive a consistent EOS including free energy and entropy information. We will discuss the relative stability of the different phases and compare methods to quantify anharmonic effects in the solid phases at elevated temperatures.