The phonon band structures comprise 3N bands (N: number of atoms) describing three acoustic modes starting from zero energy (ω = 0) at the  point (BZ center) reaching up to a few THz, 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 novel C 20 allotrope is dynamically stable, alike diamond. In both panels the highest bands are observed around ~40 THz close to the value observed for diamond by Raman spectroscopy , letting confirm the relationship with diamond for C 20 . Further support is brought from the analysis of the thermal properties.