Protomene : A new carbon allotrope

We introduce a new carbon allotrope named protomene. Its crystal structure is hexagonal, with a fully-relaxed primitive cell involving 48 atoms. Of these, 12 atoms have the potential to switch hybridization between sp2 and sp3, forming dimers. By means of DFT simulations, we have identified the equilibrium structure of protomene, and estimate that it is 2% less bound than diamond. We have also estimated the amplitude of its direct band gap to be 3 eV, and predicted the X-ray diffraction pattern and phonon modes.