The calculated stability region is larger than what has been reported in literature so far. The larger stability region in our work mainly results from different U parameters, resulting in different Gibbs free energy of formation values of the binary iron and copper oxides. Furthermore, it is important to note that the selected U parameter for Cu and Fe in the ternary copper oxide may not be optimal for their respective metallic phases, as these parameters are primarily chosen for the CFO phase. Besides, in these papers diverse Fe:Cu stoichiometric phases, liquid phases, and solid spinel phases have also been considered, while here we concentrate on the solid stoichiometric phases only. Moreover, the overbinding issue of GGA for the oxygen molecule has not been addressed in our work, which would influence the Gibbs free energy of formation for the bulk oxides as well. However, the relative stability of competing phases is in agreement with literature. Most articles describe phase diagrams for Bi 2 O 3 -CuO systems or similar two-or threecomponent systems. They all consider different stoichiometric mixtures and liquid phases, making it difficult to compare the same stability region of solid stoichiometric CBO.