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 imp urity sites in ionic crystals TiO2, Al2O3 and CaCO3. The electronic structu re was calculated self-consistently by the KKR method in the framework of t he local spin density approximation of the density functional theory. The s ystem 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 deter mination of the implantation sites of N and O nuclei in TiO2. The calculati on of EFGs at a Si impurity in Al2O3 and at Ca site in CaCO3 were used to d erive the quadrupole moments of Si-27 and Ca-39 from their quadrupole coupl ing constants.