Pymatgen (version 2020.12.31) was used to investigate the magnetic ordering of the bulk structure. Additional calculations were performed using the HSE06 hybrid functional on the ferrimagetic ground state LMNO structure (Mn↑ Ni↓) to compare with the PBEsol + U results. A denser Γ-centered 4 × 4 × 4 k-point mesh was used to produce the electronic density of states (DOS) and band structure (path from Bradley and Cracknell 47 ). Defect calculations were conducted using the PBEsol + U functional on a cubic 2 × 2 × 2 (448-atom) supercell with Γ-only k-point grid. Performing calculations using hybrid functional would be practically infeasible with our chosen supercell size due to the exorbitant computational cost. The ferrimagnetic spin configuration was initialised for all defects with fixed-volume relaxations. The force tolerance was raised to 2 × 10 -2 eV Å-1 for interstitial defects. Defect calculations set up and analysis were facilitated by DOPED. A lean version of the ShakeNBreak 52 approach was used to aid the location of the ground-state defect structures. Notably, standard defect relaxations without this symmetry breaking were found to give higher-energy metastable structures (often without correct polaronic localisation) for many defects. Displacement distributions with standard deviations of 0.02 Å and 0.05 Å were tested on individual defect structures and the lowest energy relaxed structures were taken for further analysis. Climbing-image nudged elastic band (cNEB) method was used to calculate point defect migration barriers. All crystal structure diagrams were prepared using VESTA.