Electronic, magnetic properties and correlation effects in the layered   quaternary iron oxyselenide Na2Fe2Se2O from first principles
  By means of the first-principle calculations, we have investigated electronic, magnetic properties and correlation effects for the newly discovered layered oxyselenide Na2Fe2Se2O. Our results reveal that the electron correlations in the Fe 3d bands promote a transition of Na2Fe2Se2O from magnetic metallic or half-metallic states to the antiferromagnetic Mott-insulating state. In addition, the bonding picture in Na2Fe2Se2O is described as an anisotropic mixture of ionic and covalent contributions. 
D. V. Suetin, I. R. Shein, A. L. Ivanovskii
cond-mat.mtrl-sci