Prediction of Fe-Mg and Fe-Mg-O compounds at exoplanetary interior pressures

Terrestrial exoplanets are of great interest for being geochemically and geophysically similar to Earth. Their major elements abundances are expected to be similar to Earth’s but their internal pressure and temperature conditions can vary significantly in first order with their masses/sizes. Despite much recent progress in identifying the nature of magnesium silicates up to and beyond ~3 TPa, a most important element, iron, has not been systematically included in these studies so far. Here, we use the adaptive genetic algorithm (AGA) to predict several unreported stable crystalline phases in the binary Fe-Mg and ternary Fe-Mg-O systems up to pressures at 1 TPa and 3 TPa. Analyses of local packing motifs of the low-enthalpy Fe-Mg and Fe-Mg-O phases reveal that both Fe-Mg and Fe-Mg-O systems favor BCC-like motifs at ultra-high pressures regardless of chemical composition. Our results extend the current knowledge of structural information of the Fe-Mg and Fe-Mg-O systems to exoplanetary pressures.