The electronic structures of ${\mathrm{Sr}}_2$${\mathrm{CuO}}_2$${\mathrm{F}}_2$, ${\mathrm{Sr}}_2$${\mathrm{CuO}}_2$${\mathrm{Cl}}_2$, and ${\mathrm{Ca}}_2$${\mathrm{CuO}}_2$${\mathrm{Cl}}_2$ are investigated by means of the full-potential linear muffin-tin orbital method. As in other high-${\mathit{T}}_{\mathit{c}}$ cuprates, the electronic structures of these compounds display strong two-dimensional features including a low density of states at ${\mathit{E}}_{\mathit{F}}$ 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.

• Received 3 October 1994

DOI:https://doi.org/10.1103/PhysRevB.51.6675