It is shown that iron possesses an energy band with Bloch functions which can be unitarily transformed into optimally localized Wannier functions belonging to a corepresentation of the magnetic group ${M=I4/mm}^{\prime }{m}^{\prime }$ of ferromagnetic iron. As compared to the other bands of iron, this “ferromagnetic band” is extremely narrow. In paramagnetic iron, it is roughly half-filled, and in ferromagnetic iron, it is nearly empty for the minority-spin states and nearly filled for the majority-spin states. These findings can be interpreted within the group-theoretical nonadiabatic Heisenberg model as proposed by the author for better understanding of superconductivity and spin-density-wave states. In the framework of this model, the localized states in the Heisenberg model are no longer represented by atomic or Wannier functions but by more realistic nonadiabatic localized functions which have the same symmetry as the Wannier functions. The related nonadiabatic Hamiltonian $H^n$ has the correct symmetry of the ferromagnetic state because it does not commute with the operator K of time inversion. From the symmetry of $H^n$ it follows that the ground state $|G^n〉$ of $H^n$ possesses a spin structure with the magnetic group M. Furthermore, it is argued that an operator commuting with K only has nonmagnetic eigenstates. Hence, there is evidence that the ferromagnetic band causes the stability of the ferromagnetic state in iron.

• Received 8 May 1998

DOI:https://doi.org/10.1103/PhysRevB.59.13795