Starting from the fully inverse cation configuration presents a much more difficult challenge for the methodology. The fully inverse structure for both MnFe 2 O 4 and ZnFe 2 O 4 are the furthest cation configurations from the ground state and so present a worst-case scenario for looking at unknown phase fields. The distribution of structures in terms of degree of inversion (Table ) also presents a challenge as there are far fewer low inversion structures than there are high inversion structures which makes finding the normal ground state difficult at any composition.