Ab Initio Investigation of the Cooperative Diffusion in Body-Centered Cubic Iron Under Inner Core Conditions of Earth and Super-Earth Exoplanets

In the decades old scientific controversy of the most stable phase of iron at the Earth’s inner core (IC) conditions, the thermodynamic stability of the body-centered cubic (bcc) phase is recently suggested due to cooperative diffusion of atoms in the (110) plane.^1,2 In this presentation, we provide new, in-depth understandings of the mechanism of cooperative diffusion by using ab initio molecular-dynamics simulations. Our studies find the cooperative diffusion operates along the 〈111〉 direction, which offers the least energy barrier. Even with relatively small cells, we have been able to capture cooperative diffusion in bcc iron in Earth’s IC conditions. We also find bcc iron can be stabilized by phonon interactions and facilitated by electron thermal effects. Our calculations at higher pressures (super-Earth core conditions) have yielded similar results. These results provide important insights and useful knowledge for future experimental and theoretical studies of iron under extreme pressures and temperatures that are greatly relevant to high-energy-density and planetary sciences.

1. A. B. Belonoshko et al., Nature Geosci. 10, 312 (2017).

2. A. B. Belonoshko et al., Phys. Rev. B 104, 104103 (2021).