How are light elements present in Earth’s core? An ab initio systematic exploration.

The composition of the light-element phase of the Earth's inner core remains controversial. In the present work we perform a systematic ab initio study of the possible forms that this light-element phase can show at the conditions of the inner core, including Fe_nX (n=1...5; X=S,Mg,H,C,O) compounds. We have performed automated crystalline structure searches for Fe_nX compounds using CALYPSO, and relaxed the candidate structures using VASP. We plotted the convex hulls for the compounds of Fe with each light element, and found the thermodynamically stable compounds at the conditions of the inner core. We calculated their thermal properties and density using phonon analysis and a quasi-harmonic approximation. We finally estimated the maximum abundance of the light elements in the core by comparing their compounds' densities with pure bcc-Fe and the actual density of the inner core. The results are consistent with literature findings for the outer core.(1)

1. Badro J, Cote AS, & Brodholt JP (2014) A seismologically consistent compositional model of Earth's core. Proceedings of the National Academy of Sciences of the United States of America 111(21):7542-7545.