Stability of iron crystal structures at 0.3-1.5 TPa

- Electronic structure calculations find bcc-phase in Fe mechanically unstable from 0.3 to 1.5 TPa.
- AIMD simulations for tetragonal and orthorhombic distortions follow electronic structure calculations.
- Theory and experiment document the stability of hcp-Fe at pressures of 0.3-1.5 TPa and 7000 K.
- Elastic constants of hcp Fe with deformation mechanisms can explain seismic structure of Earth's core.

Ab initio molecular dynamics simulations carried out for tetragonal and orthorhombic distortions of iron closely follow the results of static-lattice electronic-structure calculations in revealing that the body-centered cubic (bcc) phase of Fe is mechanically unstable at pressures of 0.3-1.5 TPa and temperatures up to 7000 K. Crystal-structural instabilities originate in the static lattice for the bcc configuration, and are consistent with recent results from both static and dynamic high-pressure experiments. Both theory and experiment thus show that the close-packed (hexagonal, hcp and face-centered cubic, fcc) crystal structures of iron are those relevant to the cores of Earth-like planets.