From the ground state structures the sets of elastic constants C ij were calculated, and the mechanical properties such as hardness and fracture toughness were estimated using contemporary theoretical models. To verify the dynamic stability of different phases, the phonon dispersion bands were calculated. The approach consists of computing the phonon modes through finite displacements of the atoms off their equilibrium positions to subsequently obtain the forces from the summation over the different configurations. The phonon dispersion curves along the main lines of the tetragonal Brillouin zone (BZ) were obtained using first-principles phonon calculation code "Phonopy" .