  Being a lithophile element at ambient pressure, magnesium is long believed to
be immiscible with iron. A recent study by Gao et al. [1] showed that pressure
turns magnesium into a siderophile element and can produce unconventional Fe-Mg
compounds. 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.
Our cluster alignment analysis reveals that most of the predicted Fe-Mg
compounds prefer a BCC packing motif at terapascal pressures. This study
provides 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.
