Unrestricted Hartree-Fock approach to the insulating behavior of antiferromagneticCaCuO2

Ground-state properties of ${\mathrm{CaCuO}}_2$, a parent compound of the high-${\mathit{T}}_{\mathit{c}}$ superconductors, are calcula- ted ab initio using a LAPW spin-unrestricted Hartree-Fock (UHF) scheme. While ${\mathrm{CaCuO}}_2$ is a metal within the local-spin density approximation, UHF retains the essential nonlocality of exchange, and predicts a wide gap insulator with an antiferromagnetic moment μ≊0.8${\mathrm{\mu }}_{\mathit{B}}$. Results for hypothetical ferromagnetic ${\mathrm{CaCuO}}_2$ indicate that the insulating character does not depend on the magnetic ordering. The shortcomings of UHF are corrected in part with a simple diagonal-screening model.