Unconventional iron-magnesium compounds at terapascal pressures

Being a lithophile element at ambient pressure, magnesium has been long believed to be immiscible with iron. Authors of a recent study showed that pressure turns magnesium into a siderophile element and can produce unconventional Fe-Mg compounds [Gao et al., New J. Chem. 43, 17403 (2019)]. Here, we extend the investigation to exoplanetary pressure conditions using an adaptive genetic algorithm-based variable-composition structural prediction approach. We identify several Fe-Mg phases up to 3 TPa at 0 K. Our cluster alignment analysis reveals that most of the predicted Fe-Mg compounds prefer a body-centered cubic packing motif at terapascal pressures. In this paper, we provide a more comprehensive structure database to support future investigations of the high-pressure structural behavior of Fe-Mg and ternary, quaternary, etc. compounds involving these elements.