  Earth's inner core consists of mainly iron with a bit of light elements.
Understanding of its structure and related physical properties has been elusive
for both experiment and theory due to its required extremely high pressure and
temperature conditions. Here, using density functional theory plus dynamical
mean field theory, we demonstrate that oxygen atoms energetically stabilize
hexagonal structured iron at the inner core condition. Electrical resistivity
is much enhanced compared with pure hcp-Fe, supporting the conventional thermal
convection model. Moreover, our calculated seismic velocity shows a
quantitative match with geologically observed Preliminary Reference Earth Model
data.
