First-principles calculations of hyperfine interactions in La2CuO4

We present the results of first-principles cluster calculations of the elec tronic structure of La2CuO4. Several clusters containing up to nine copper atoms embedded in a background potential were investigated. Spin-polarized calculations were performed both at the Hartree-Fock level and with density -functional methods with generalized-gradient corrections to the local-dens ity approximation. The distinct results for the electronic structure obtain ed with these two methods are discussed. The dependence of the electric-hel d gradients at the Cu and the O sites on the cluster size is studied and th e results are compared to experiments. The magnetic hyperfine coupling para meters are carefully examined. Special attention is given to a quantitative determination of on-site and transferred hyperfine fields. We provide a de tailed analysis that compares the hyperfine fields obtained for various clu ster sizes with results from additional calculations of spin states with di fferent multiplicities. From this we conclude that hyperfine couplings are mainly transferred from nearest-neighbor Cu2+ ions and that contributions f rom further distant neighbors are marginal. The mechanisms giving rise to t ransfer of spin density are worked out. Assuming conventional values for th e spin-orbit coupling, the total calculated hyperfine interaction parameter s are compared with those derived from experiments.