Structure search calculations in NiO 2 were run in a supercell generated to best mimic a cubic-like cell while maintaining a minimum lattice vector 10 A in each direction. The twin boundary structure was taken from ref , and expanded to minimize interactions between periodic images. Structure search calculations run with "coarse" settings: Γ-point only k-point sampling and a force convergence tolerance of 0.02 eV/ Å. Any structures which were then discussed further were then re-relaxed with 2×2×2 k-point mesh and a force convergence criteria of 0.01 eV/ Å (excepting the twin boundary structures, which were relaxed with DFT+U followed by only coarse HSE06 calculations).