Crystal structure prediction for iron as inner core material in heavy terrestrial planets

The relative stability of different crystal structures for pure Fe under applied pressure is calculated from quantum mechanics, using the highly accurate APW + lo method. In the pressure range of 0–100 TPa, we corroborate the prediction that iron adopts subsequently the bcc, hcp, fcc, hcp and bcc structures. In contrast to previous studies, we identify a family of stacking fault structures that are competing with the ground state structure at all pressures. Implications for the properties of the inner core of the Earth and heavy terrestrial exoplanets are discussed.

► Pure iron up to 100 TPa goes through the bcc–hcp–fcc–hcp–bcc structure sequence.
► The reliability of previously suggested high-pressure pseudopotentials is confirmed.
► Crystal structure prediction tools reveal the relevance of stacking faults.
► Properties of stacking fault structures under pressure are systematically studied.
► The material in terrestrial inner cores might contain lots of stacking faults.