First-principles calculation of electric field gradients and hyperfine couplings in YBa2CU3O7

The local electronic structure of YBa2Cu3O7 has been calculated using first -principles cluster methods. Several clusters embedded in an appropriate ba ckground potential have been investigated. The electric field gradients at the copper and oxygen sites are determined and compared to previous theoret ical calculations and experiments. Spin polarized calculations with differe nt spin multiplicities have enabled a detailed study of the spin density di stribution to be made and a simultaneous determination of magnetic hyperfin e coupling parameters. The contributions from on-site and transferred hyper fine fields have been disentangled with the conclusion that the transferred spin densities essentially are due to nearest neighbour copper ions only w ith marginal influence of ions further away. This implies that the variant temperature dependencies of the planar copper and oxygen NMR spin-lattice r elaxation rates are only compatible with commensurate antiferromagnetic cor relations. The theoretical hyperfine parameters are compared with those der ived from experimental data.