Ab initio calculations of electric field gradients detected by impurities in TiO2,Al2O3 and CaCO3

We present ab initio calculations of electric field gradients (EFGs) at impurity sites in ionic crystals TiO2, Al2O3 and CaCO3. The electronic structure was calculated self-consistently by the KKR method in the framework of the local spin density approximation of the density functional theory. The system with a single impurity was simulated by the super cell method. It was found that EFGs for the transition metal impurities (Sc, Nb, Cd and Ta) in TiO2 were well reproduced by the calculations if the charge state of them in TiO2 was taken into account. The present method was applied to the determination of the implantation sites of N and O nuclei in TiO2. The calculation of EFGs at a Si impurity in Al2O3 and at Ca site in CaCO3 were used to derive the quadrupole moments of Si-27 and Ca-39 from their quadrupole coupling constants.