To verify the dynamical stability of the predicted phases, their phonon properties were studied. The phonon band structures (red lines) obtained according to the protocol presented in section 2 are shown in Fig. . The horizontal direction corresponds to the main directions of the hexagonal Brillouin zone, while the vertical direction shows the frequencies ω, given in terahertz (THz). The absence of negative frequencies indicates dynamically stable phases. The band structure includes 3N bands with 3N-3 optical modes found at higher energies than three acoustic modes starting from zero energy (ω = 0) at the  point, the center of the Brillouin zone, up to a few terahertz. They correspond to the lattice rigid translation modes of the crystal (two transverse and one longitudinal).