Structural Distortion Stabilizing the Antiferromagnetic and   Semiconducting Ground State of BaMn$_2$As$_2$
  We report evidence that the experimentally found antiferromagnetic structure as well as the semiconducting ground state of BaMn$_2$As$_2$ are caused by optimally-localized Wannier states of special symmetry existing at the Fermi level of BaMn$_2$As$_2$. In addition, we find that a (small) tetragonal distortion of the crystal is required to stabilize the antiferromagnetic semiconducting state. To our knowledge, this distortion has not yet been established experimentally. 
Ekkehard Kr\"uger
cond-mat.str-el