High-pressure characteristics of alpha-Fe2O3 using DFT plus U

We have calculated the structural, magnetic and electronic properties of corundum-type alpha-Fe2O3 from first principles using density-functional theory (DFT) and the DFT + U method to account for correlation effects in this material. Although the correct magnetic ground state is obtained by pure DFT, the magnetic moments and the band gap are too small, and the predicted structural phase transition coupled with a transition from the insulating high-spin to a metallic low-spin phase at a pressure of 14 GPa is not observed experimentally. We find that considering the Coulomb interaction directly by including a Hubbard-like term U in the density functional greatly improves the results with respect to band gap and magnetic moments. The phase transition is shifted to higher pressures with increasing values of U and disappears for U > 3 eV. The best overall agreement of structural, magnetic and electronic properties with experimental data is obtained for U = 4eV.