Sensible random structures were first generated with pre-assumed ferromagnetic (FM) spin states and then geometry optimized by the plane-wave DFT CASTEP code ). Spinpolarized calculations were performed using the PBEsol exchange-correlation XC functional with Hubbard U correction (U eff = 6 eV) for Ni d electrons (i.e. PBEsol+U). Geometry optimizations were initially performed with a loose convergence setting (i.e. crude search).