The thermal properties such as heat capacity at constant volume C v were calculated using the statistical thermodynamic expressions from the phonon frequencies on a high precision sampling mesh in the BZ . Figure shows the temperature change of heat capacity at constant volume C v for the three allotropes. The experimental values for diamond are shown with symbols. As a general trend 'glitter' and 'isoglitter' allotropes have higher C v than 'metaglitter', while the experimental values for diamond sit on the C v curve of the latter.