The SCAN+U method in the investigation of complex transition metal oxides: a case study on YSr₂Cu₂FeO₇₊ (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 YSr₂Cu₂FeO₇₊ (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 YSr₂Cu₂FeO₇ phase, while maintaining the metallic characteristics of YSr₂Cu₂FeO₈. 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.