Using the crystal parameters in Table , the electronic band structures were obtained using the allelectrons DFT-based augmented spherical method (ASW) and are shown in Figure . The bands develop along the main directions of the primitive tetragonal Brillouin zones. As all four systems are characterized with a band gap between the valence band (VB) and the empty conduction band (CB), the energy reference along the vertical energy axis is with the respect to the top of the VB.