First-principles study of the melting curve of iron

The phase diagram of iron at high pressure is of considerable interest for geophysics and planetary science. The interior structure of rocky planets, such as the size and state of the core and related core-formation processes, depend on the detailed behavior of planetary materials, such as iron, at high pressure and temperature. Using density functional theory molecular dynamics, we investigate the melting curve of iron at megabar pressures. We derived the melting temperature by equating the Gibbs free energies of solid and liquid phases that we derived through the thermodynamic integration method. The melting curve allows us to study the crystallization behavior of iron under high compression. Our calculations show that the melting temperatures of iron are higher than extrapolations from previously calculated melting curves at lower pressures. Finally we compare its slope with the adiabatic gradient in order to determine how the cores of super-Earth planets crystallize.