In general, after a large investigation of periodic and non-periodic Ni-N-C models in VASP and ORCA code correspondingly, we have found that all the square planar structures strongly prefer (~ -1 eV) a low spin (LS) state (〈𝑆〉=0, singlet) than any other spin state, and resist out-of plane deformations of the Ni-center, regardless of the DFT+U or and hybrid-DFT approach used (see Theoretical Calculations Details). Only when we allow for tetrahedrally distorted NiN4 structures (D2d symmetry), Ni energetically prefers (~ -0.2 eV) to be in a high spin (HS) state (〈𝑆〉=1), as shown in Figure . In this figure, we also show that optimal structures consist of dihedral angle between planes 153° to 123°. The low spin state of Ni is energetically more favorable over high spin, only for a square-planar geometry (dihedral angle of 180°).