Hybrid density functional theory study of the high-pressure polymorphs ofα-Fe2O3hematite

Abstract

The relative stability with respect to pressure of four structural polymorphs of Fe 2 O 3 has been studied using the B3LYP hybrid exchange density functional theory, and for each polymorph a range of charge, spin, and magnetic states were examined. It was found that the B3LYP functional computed charge, magnetic ordering, structural, and elastic properties of corundum structure Fe 2 O 3 are in good agreement with experiment. Magnetic ordering was found to be important for all the polymorphs, and for each polymorph antiferromagnetic ordering was found to be lower in energy than ferromagnetic ordering. The Rh 2 O 3 -II structure was calculated to be metastable, with the transition pressure from the corundum structure and the pressure at which magnetic collapse of Fe 3+ cations occur in good agreement with experiment. At high pressures the lowest-energy configuration for the orthorhombic perovskite structure was computed to occur with mixed high-spin/low-spin Fe 3+ cations. The CaIrO 3 -type structure was also computed to be stable with a mixed high-spin/low-spin Fe 3+ configuration at high pressures, and is computed to be the most stable polymorph at pressures above 46 GPa at 0 K. Overall we predict a number of phase-transition pressures which have been experimentally observed and give some insight into the mechanisms underlying the structural transformations.

Microwave Permittivity, Permeability, and Absorption Capability of Ferric Oxide

“…These results are consistent with the fact that Fe2O3 becomes weakly ferromagnetic above the Morin transition at -13°C and below its Néel temperature at 675°C. 12,13) Continuous heating to higher temperatures gives rise to different variation behaviors of μr' and μr". The μr'…”

Influence of Strong Electron Correlation on Magnetism in Transition-Metal Doped Si Nanocrystals

“…[27][28][29][30] Also, ferromagnetic systems may be modeled using such an approach. 31 The idea is, however, not to include simply the nonlocal Hartree-Fock exchange in which no correlation part is present. Rather, the use of a spatially nonlocal XC potential in the Kohn-Sham equation is considered as a zeroth-order approximation for the XC self-energy of the quasiparticle equation.…”

Efecto del intercambio exacto sobre el Band Gap en óxidos metálicos

“…In the same way, Pozun and Henkelman [26] decreased the EEX for the HSE06 exchange-correlation functional and improved the band gap value, as we have discussed above. We remark these reports since HSE06 and B3LYP XC functionals predict one p-d gap [99,100], which is consistent with our results. The present discussion has been around spin up; however, same conclusion can be reached when spin-down DOS is analyzed in the same way.…”