Electric field gradients in cuprates:: Does LDA+U give the correct charge distribution?

We present calculations for the electric field gradients (EFG) on the Cu sites in La2CuO4, YBa2Cu3O6, and YBa2Cu3O7 using standard LDA and GGA exchange-correlation functionals, but also by using the LDA+U method for the correlated Cu-d electrons. LDA or GGA calculations yield proper EFGs in agreement with experiment for all sites except the planar Cu(2) site, where the theoretical EFGs are too small by a factor of 2 to 3. This happens for both the metallic (superconducting) YBa2CU3O7 and the antiferromagnetic insulators. For the latter, these calculations also lead to a nonmagnetic and metallic solution. Application of LDA+U with various double-counting corrections and varying values for the Hubbard parameter U gives the correct magnetic and insulating ground state and the corresponding EFGs are substantially enhanced. Best agreement with experiment is found using the LDA+U(FLL) method with U around 6eV, because this method leaves the Cu(1) EFG unchanged, even when U is applied to its d-states. For the metallic compound YBa2Cu3O7, the EFG results favor the presence of local magnetic moments; however, in bandstructure calculations the necessary long-range order leads to some artifacts and should be replaced by random spin fluctuations. (C) 2004 Wiley Periodicals, Inc.