Electric field gradients, isomer shifts and hyperfine fields from band structure calculations in NiI2

NiI2 undergoes an isostructural phase transition under pressure from an insulating antiferromagnetic state to a metallic but nonmagnetic state. We investigate this transition with the full-potential linearized augmented plane wave (LAPW) method within the density functional theory using the generalized gradient approximation (GGA), which provides an improved description of exchange and correlation effects. Once the electron density is calculated self-consistently with high accuracy, quantities such as electric field gradients, isomer shifts or hyperfine fields can easily be obtained from that density. Using this approach we study the change of the iodine hyperfine parameters during the pressure induced metallization of NiI2. In general, good agreement between theory and experiment is found, and insight is gained by an analysis of the theoretical data indicating the physical origin of the measured quantities. (orig.)