New transitions of MgSiO3 post-perovskite under ultrahigh pressure*

Understanding the behavior of MgSiO$_{3}$ post-perovskite (PPV) under extreme pressures is fundamental for modeling the interiors of super-Earth type exoplanets and the cores of solar giants. Previously, MgSiO$_{3}$ PPV was predicted to dissociate into MgO and MgSi$_{2}$O$_{5}$ and then into MgO and SiO$_{2}$ (Umemoto et al., Science 311, 983 (2006); Umemoto and Wentzcovitch, EPSL 311, 225 (2011)). Using the adaptive genetic algorithm, we predict new phase transitions in MgSiO$_{3}$. The phase diagram calculated using the quasi-harmonic approximation shows that some transitions can occur in some super-Earths type exoplanets.