There are 3X 4-fold rotation axes. These axes can be chosen as starting from the original FeI in a unit cell to its adjacent FeI’s in the same unit cell. These constitute a PAS and the EFG is the zero tensor due to the second part of theorem 1.
1X 4-fold rotation axis pointing from FeII toward N.
2X 2-fold rotation axes pointing from FeII towards a FeI.
This constitutes a PAS with the 4-fold being the z-axis. The EFG has axial symmetry.