The Fe-I atoms have 3 perpendicular 4-fold rotation axes so each of them can be chosen as the z-axis in the PAS and η=0 according to theorem 1. According to theorem 2 the EFG tensor is then zero. The Fe-II atoms have 1 4-fold rotation axis, the z-axis and 2 2-fold axes, x- and y-axis. The z-axis can then be chosen as the z-axis of the PAS and the η=0 but the EFG is not zero since there is no multiple 3-fold axes.