Application of the GGA-1/2 excited-state correction method to p-electron defective states: the special case of nitrogen-doped TiO2

Abstract

One of the issues in applying the generalized gradient approximation–1/2 (GGA-1/2) quasiparticle approximation to correct the excited-state properties in defective semiconductors is determining the cutoff to the self-energy function at the point defect. Pure and large supercells of N-doped rutile TiO2 were studied using this method to correct excited states and find the correct position of the defect states. A relation between the Bader charge at the defect and the self-energy cutoff parameter of the GGA-1/2 method is shown, with the cutoff value in its p-orbital, which optimizes the position of the defect levels. It was found that, upon nitrogen substitution and associated oxygen vacancy formation, an impurity level at 0.40–0.52 eV above the valence band maximum appears. The same result was obtained upon nitrogen substitution and associated background charge. Finally, the method was also applied to other p-orbital defect systems like Si:X (X = N, P, B) to validate the method.