The activation barriers for vacancy diffusion between adjacent O1 sites within the La4Ni3O10, Pr4Ni3O10 and L2P2N3 structure were calculated using the climbing image nudged elastic band approach (CI-NEB) . To minimise the interactions between vacancies in adjacent cells, 2×2×1 supercells of the initial primitive Bmab unit cells were created. A single vacancy was introduced into the supercell (M32Ni24O79) into neighbouring O1 sites, and the atomic positions were optimised under fixed cell conditions to a force tolerance of 0.01 eV Å -1 . CI-NEB were performed with 5 intermediate images under fixed cell condition using same force tolerance.