Optimal <i>U</i> values for 3<i>d</i> transition metal oxides within a SCAN+<i>U</i> framework

Redox-active transition metal oxides that can tolerate oxygen off-stoichiometry are crucial ingredients for generating renewable fuels via oxide-based solar thermochemical reactors. However, any predictive modeling, such as using density functional theory (DFT) calculations, needs to accurately describe the energetics of redox reactions involving transition metals, if new candidates are to be found. Recently, we found that the strongly constrained and appropriately normed (SCAN) exchange-correlation functional requires a Hubbard U correction (determined, e.g., from experimental oxidation enthalpies) to accurately describe the ground state structure, magnetic moments, and electronic properties of Ce-, Mn-, and Fe-based systems. In the present work, we extend our approach to identify optimal U values for other 3d oxides within the SCAN+U framework. Although the absolute magnitude of U values required for all 3d metals is lower than what is needed using a generalized gradient approximation+U or a local density approximation+U approach, we find that the addition of U makes non-negligible improvements in ground state property predictions, particularly for Ti, V, Co, and Ni oxides, highlighting the importance of using a SCAN+U framework.