Electronic structure of superconductors without apical oxygen: Sr2CuO2F2, Sr2CuO2Cl2, and Ca2CuO2Cl2

The electronic structures of Sr2CuO2F2, Sr2CuO2Cl2, and Ca2CuO2Cl2 are investigated by means of the full-potential linear muffin-tin orbital method. As in other high-Tc cuprates, the electronic structures of these compounds display strong two-dimensional features including a low density of states at EF and a simple Fermi surface of the form of a rounded square. A major van Hove saddle-point singularity exists near the Fermi level. We predict the optimum superconductivity properties in these materials to occur when doped by 0.35-0.38 holes per unit cell.