Revisiting the Nitrogen Doping in Crystalline and Amorphous TiO 2

In this work, we present a comprehensive methodological study of a well‐known defect in TiO 2 , namely substitutional nitrogen on oxygen sites (N O ), with the primary focus placed on a comparative assessment of three different electronic‐structure approaches across both crystalline and amorphous phases. While N‐doped TiO 2 has been extensively investigated in the literature, a systematic comparison of theoretical methods that simultaneously addresses the main crystalline polymorphs—anatase and rutile—and amorphous titania is still lacking, particularly for the latter, where quantitative data remain scarce. Starting from standard density functional theory (DFT), we extend the analysis to the well‐assessed DFT+ U method of Lichtsteiner and finally to the recently introduced DFT‐ of Teles et al., which has the merit of perfectly reproducing the experimental bandgap of TiO 2 , and of many other semiconductors. Because the description of defect states strongly depends on an accurate electronic structure, this represents a substantial improvement over conventional DFT, which, being a ground‐state theory, systematically underestimates the bandgap. Similarities and differences among the approaches are discussed in detail.