Accurate models of the interior structure of planetary bodies, in our or other solar systems, are key to understanding their formation and many of their properties. For instance, the stratification (or lack thereof) of molecular mixtures inside icy planets’ mantles influences their luminosity and cooling rates; and the presence (or not) of water stored inside rocky planets’ mantles influences their convection rates, the magnitude of plate tectonics and presence of surface water. But direct measurements of planetary interiors are virtually impossible and laboratory experiments are difficult, which is why accurate computer simulations can make important contributions.
In my talk I will give an overview of our ongoing research aimed at a better understanding of planetary materials using electronic structure calculations. I will focus on hydrogen-containing systems and discuss the phase evolution of icy mixtures relevant inside Neptune-like bodies , and the stabilisation of new forms of hydrous minerals inside silicate-based rocky bodies .
 V. Naden Robinson, et al., Proc. Natl. Acad. Sci. 114, 9003 (2017)
 A. Hermann et al., Proc. Natl. Acad. Sci. 113, 13971 (2016)