The band structures include 3N bands: three acoustic modes starting from zero energy (ω = 0) at the  point (the center of the Brillouin zone) and reaching up to a few terahertz, and 3N-3 optical modes at higher energies. The low-frequency acoustic modes are associated with the rigid translation modes (two transverse and one longitudinal) of the crystal lattice. The calculated phonon frequencies are all positive, indicating that the four new B-N phases are dynamically stable.