The ground state FiM structure was optimised with PBEsol + U and HSE06 methods separately and the calculated (cubic) lattice constants are in good agreement with experimental data (Table ). The local coordination around Ni shows six oxygens at equal distances of 2.05 -2.06 Å. The local Mn coordination is distorted with three inequivalent Mn-O distances and is a consequence of Mn coordinating to two symmetry-inequivalent oxygens in the 24e sites (surrounded by 2Mn 4+ , Ni 2+ and Li + ) and 8c sites (surrounded by 3Mn 4+ and Li + ).