Theory of copper hyperfine interactions in theLa2CuO4system

The unrestricted Hartree-Fock cluster procedure is used to study the electronic structure of ${\mathrm{La}}_2$ ${\mathrm{CuO}}_4$ and obtain the ${}_{}{}^{63}{}_{}{}^{}\mathrm{Cu}$ quadrupole coupling constant and asymmetry parameter of 88.4 MHz and 0.04, respectively, in satisfactory agreement with experiment. A magnetic hyperfine field of 105.2 kG is obtained at the ${}_{}{}^{63}{}_{}{}^{}\mathrm{Cu}$ nucleus, as compared to 78.78 kG from experiment. The effective charges on copper and oxygen ions and the mixing of copper and planar oxygen orbitals in the wave functions suggest significant covalent bonding between them. The magnetic moment on the copper ion is reduced by the influence of the covalency effect and will be compared with experiment.