Ground state properties of the Holstein-Hubbard model
  We study the ground state properties of the Holstein-Hubbard model on some bipartite lattices at half-filling; The ground state is proved to exhibit ferrimagnetism whenever the electron-phonon interaction is not so strong. In addition, the antiferromagnetic long range order is shown to exist in the ground state. In contrast to this, we prove the absence of the long range charge order. 
Tadahiro Miyao
math-ph math.MP