Abstract
Diamond has the highest number density (i.e., the number of atoms per unit volume) of all known substances and a remarkably high valence electron density ( 0.697 Å). Searching for possible superdense carbon allotropes, we have found three structures (P3, I12, and P12) that have significantly greater density. The P3 and P12 phases have strong analogy with two polymorphs of silica (-quartz and keatite), while the I12 phase is related to the high-pressure SiS polymorph. Furthermore, we found a collection of other superdense structures based on the motifs of the aforementioned structures, but with different ways of packing carbon tetrahedra, and among these the P3 and I12 structures are the densest. At ambient conditions, the P3 phase is a semiconductor with the GW band gap of 3.0 eV, I12 is an insulator with the band gap of 5.5 eV, while P12 is an insulator, the band gap of which is remarkably high (7.3 eV), making it the widest-gap carbon allotrope. These allotropes are metastable and have comparable to diamond or slightly higher bulk moduli; their Vickers hardnesses are calculated to be 87.6 GPa for P3, 87.2 GPa for I12, and 88.3 GPa for P12, respectively, thus making these allotropes nearly as hard as diamond (for which the same model gives the hardness of 94.3 GPa). Superdense carbon allotropes are predicted to have remarkably high refractive indices and strong dispersion of light.
- Received 12 April 2011
- Corrected 7 June 2011
DOI:https://doi.org/10.1103/PhysRevB.83.193410
©2011 American Physical Society
Corrections
7 June 2011