Antiferromagnetic Insulating Energy Bands of Tetragonal Ca(Sr)CuO2

The band structures of CaCuO2 with various planar structures have been computed with Ab Initio, LDA, spin polarized, full potential and pseudofunction method. The perfect tetragonal structure has metallic bands. If the CuO plane is puckered as proposed on the basis of pulsed neutron experiments, a semimetallic like behavior is found. When some of the oxygen atoms are moved from the basal plane into interplanar sites so as to be co-layered with Ca, an insulating ground state is obtained with antiferromagnetic moments of 0.21 µB. Around this interplanar site, the charge and magnetic moment distribution resemble those of a chain structure with the Cu providing strong coupling between the basal planes. Small displacement of oxygen at the interplanar sites along the planar directions produces large changes in band shapes near Ef, suggesting strong electron-lattice coupling. The changes are much weaker for displacements of O atoms within the plane. For SrCuO2, the band structure is similar to CaCuO2, but slightly more conductive.