The SCAN+ U method in the investigation of complex transition metal oxides: a case study on YSr 2 Cu 2 FeO 7+ δ ( δ = 0, 1).

Assessment of DFT methods is essential to sustain reliability in the computational investigation of complex transition metal oxides. This work evaluates the performance of the strongly constrained and appropriately normed (SCAN) functional and its extended Hubbard- U methodology (SCAN+ U ) to model the YSr 2 Cu 2 FeO 7+ δ (0 < δ < 1) perovskite-based system. The influence of the individual U Cu and U Fe Hubbard parameters (0 < U < 4 eV) on the calculated electronic, magnetic and crystal structures of the end members δ = 1 (metallic) and δ = 0 (insulating) is analyzed. The introduction of the U -correction terms enhances the reproduction of the crystal structures, with a U Cu value of 1 eV improving the band gap accuracy for the YSr 2 Cu 2 FeO 7 phase, while maintaining the metallic characteristics of YSr 2 Cu 2 FeO 8 . At a fixed U Cu value, the results are almost insensitive to the U Fe value used in the calculations. The findings emphasize that for oxides containing several TM ions, the optimal U TM values may differ from those of the simple TM oxides.