Study of the thermodynamic stability of iron at inner core from first-principles theory combined with lattice dynamics

The stability of iron has been reevaluated by a simple but accurate scheme. A combination of self-consistent ab initio lattice dynamics (SCAILD) and the long-wave limit approximation has been applied to investigate the elastic properties of iron at inner core conditions. We demonstrate that the vibrational contribution plays a crucial role to stabilize the systems with cubic symmetry. Especially, the fcc iron will be more stable than hcp iron at the temperature above 7200 K. As for the effect of the anharmonic part, in our calculation the smaller elastic constants are obtained at high temperature compared with previous calculations. Finally, applying our results to the seismological explorations, we find that the seismological data can be explained sufficiently when conglomerating the crystal of hcp and fcc iron with different orientation of fast crystallographic axes.