The computational methodology was developed in previous works . Essentially, the search for the ground state structures with minimal energies was systematically performed using unconstrained geometry optimizations within the DFT-based Vienna Ab initio Simulation Package (VASP) using the projector augmented wave (PAW) method for potentials . The DFT exchange-correlation (XC) effects were treated using a generalized gradient approximation (GGA) . The plane wave energy cut-off was 500 eV. The study of the mechanical properties was based on the calculations of the elastic properties, which were determined by performing finite distortions of the lattice and deriving the elastic constants from the strain-stress relationship. The calculated elastic constants C ij are then used to obtain the bulk (B) and the shear (G) moduli with the Voigt averaging method based on uniform strain. In addition to the mechanical properties, the dynamic stability was determined from the phonons, which are described as vibrational quanta.