First-principles calculations on the energetics, electronic structures and magnetism of SrFeO(2).

The electronic and magnetic properties of SrFeO(2) with different magnetic configurations have been calculated via the plane-wave pseudopotential density functional theory method, using the experimental lattice parameters. The results give an antiferromagnetic ground state for SrFeO(2) with an absolute magnetic moment agreeing very well with the experimental report. In comparison with the counterparts whose magnetic moments are parallel to the c axis, the structures with spin moments parallel to the a (or b) axis exhibit no observable preference in total energy, but show different density distributions of the Fe 3d(x(2)-y(2) ) and Fe 3d(z(2) ) states. The square-planar crystal field splits the Fe 3d orbitals into a high-level d(x(2)-y(2) ), a low d(z(2) ), and intermediate d(xy) and d(xz) or d(yz) components. The exchange splitting is larger than the crystal-field splitting, resulting in the high-spin Fe 3d states. Referred to the triplet O(2), the O-vacancy formation energy from SrFeO(3) to SrFeO(2) has been deduced as well, along with its dependence on the temperature and O(2) partial pressure.