The physical state and properties of silicates at conditions encountered in the cores of gas giants, ice giants, and of Earth-like exoplanets now discovered with masses up to several times the mass of the Earth remain mostly unknown. Here, we report on theoretical predictions of the properties of silica, ${\text{SiO}}_2$, up to 4 TPa and about 20 000 K by using first principles molecular dynamics simulations based on density functional theory. For conditions found in the super Earths and in ice giants, we show that silica remains a poor electrical conductor up to 10 Mbar due to an increase in the Si-O coordination with pressure. For Jupiter and Saturn cores, we find that ${\text{MgSiO}}_3$ silicate has not only dissociated into MgO and ${\text{SiO}}_2$, as shown in previous studies, but that these two phases have likely differentiated to lead to a core made of liquid ${\text{SiO}}_2$ and solid (Mg,Fe)O.

• Received 15 March 2014
• Revised 24 May 2015

DOI:https://doi.org/10.1103/PhysRevB.92.014105