Fe4N symmetries

For the corner site we find 3 4-fold rotation axis along the edges of the crystal so the EFG tensor is zero (undefined PAS here and also eta because V_zz=0). It also has 2-fold rotations on the diagonals of the faces of the cube and 3-fold rotations on the body-diagonals.
For the face-centered site the rotation axis going through nitrogen is 4-fold and is thus the z-axis of the PAS and makes eta = 0. It also has two two-fold rotation axis along the lines connecting it to red atoms on the same face.