All DFT calculations were performed using the plane-wave DFT Vienna Ab Initio Simulation Package (VASP) . Valence electrons were described by a plane-wave basis set with a cutoff of 680 eV. Interactions between core and valence electrons were described using the projector-augmented wave (PAW) method . Electronic exchange and correlation were approximated using the Perdew-Burke-Ernzerhof functional, revised for solids and surfaces (PBEsol) with rotationally averaged Hubbard U corrections of 3.9 eV, 3.7 eV, 5.3 eV, 6.2 eV and 4.2 eV applied to the Mn, Cr, Fe, Ni and Ti 3d orbitals respectively to approximately correct for the self-interaction error (SIE) . Reciprocal space was sampled with a discretisation of 0.35 Å -1 . All calculations were initialised with transition metal ions in a ferromagnetic configuration.