The identification of the ground state structures corresponding to the energy minima and prediction of their mechanical and dynamical properties were carried out by DFT-based calculations using the Vienna Ab initio Simulation Package (VASP) code and the projector augmented wave (PAW) method for the atomic potentials. Exchange correlation (XC) effects were considered using the generalized gradient functional approximation (GGA) . The relaxation of the atoms to the ground state structures was performed with the conjugate gradient algorithm according to Press et al. . The Blöchl tetrahedron method with corrections according to the Methfessel and Paxton scheme was used for geometry optimization and energy calculations, respectively.