Temperature of the inner-core boundary of the Earth: Melting of iron at high pressure from first-principles coexistence simulations

The Earth’s core consists of a solid ball with a radius of 1221 Km, surrounded by a liquid shell which extends up to 3480 km from the center of the planet, roughly half way toward the surface the mean radius of the Earth is 6373 km . The main constituent of the core is iron, and therefore the melting temperature of iron at the pressure encountered at the boundary between the solid and the liquid the inner-core boundary ICB provides an estimate of the temperature of the core. Here I report the melting temperature of Fe at pressures near that of the ICB, obtained with first-principles techniques based on density-functional theory. The calculations have been performed by directly simulating solid and liquid iron in coexistence and show that and at a pressure of 328 GPa iron melts at 6370 100 K. These findings are in good agreement with earlier simulations, which used exactly the same quantum-mechanics techniques but obtained melting properties from the calculation of the free energies of solid and liquid Fe.