An important criterion of phase stability is obtained from the phonon's properties. Phonons are quanta of vibrations; their energy is quantized by the Planck constant 'h' which is used in its reduced form ћ (ћ = h/2π), giving the phonons energy: E = ћω (frequency: ω) All four carbon allotropes were subjected to phonon studies to determine their respective dynamic properties. Fig. shows the phonon bands. In the horizontal direction, the bands develop along the main lines of the hexagonal Brillouin zone (reciprocal k-space). The vertical direction shows the frequencies ω, which are given in terahertz (THz) units.