Electric-field gradients in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$: Discrepancy between experimental and local-density-approximation charge distributions

Local-density-approximation (LDA) -based calculations of electric-field gradients (EFG’s) for ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_7$ using an extended linearized-augmented-plane-wave method are reported. This extended method controls errors that might arise from extended core states on the Y ions or linearization of the narrow 3p states. The calculated EFG’s agree well with experiment except for the plane Cu site. For this site a large discrepancy is found, which is attributed to an inadequate description of anisotropic effects within the LDA.