Theoretical X-ray absorption near-edge structure signatures of solid and liquid phases of iron at extreme conditions

X-ray absorption near-edge spectroscopy (XANES) spectra of solid and liquid iron at pressure and temperature obtainable at the Earth's mantle conditions have been calculated. The spectra have been obtained using the supercell with an electron core-hole approach, in an ab initio scheme based on the continued-fraction approach and norm-conserving pseudo-potentials. The atomic structures for the spectra calculations were obtained from classical molecular dynamics simulations performed using an optimized modified embedded-atom potential. Comparisons to experimental XANES data are made for both solid and liquid phases of iron. For the liquid configuration, we find excellent agreement. Calculated spectra obtained for the solid configurations are also in good agreement with the experiment, and those obtained via other theoretical methods. We discuss the electronic origin of the XANES features.