  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.
