Two-dimensional materials with Dirac cones: Graphynes containing heteroatoms
Two graphynes, 6(H2),14,18 graphyne and 6BN,6,12 graphyne, that contain the heteroatoms hydrogen or boron and nitrogen, respectively, are shown to feature Dirac points in their band structure according to first-principles electronic structure calculations. This shows that the existence of Dirac points in the band structure of two-dimensional materials is neither restricted to graphene nor to other two-dimensional all-carbon materials. 6(H2),14,18 graphyne and 6BN,6,12 graphyne belong to the rectangular two-dimensional space groups pmm and pm, respectively, and thus exhibit completely different symmetries than graphene. 6BN,6,12 graphyne features a Dirac cone with a band gap originating from an avoided crossing of its valence and conduction band at the Dirac point due to missing reflection symmetry. The examples of 6(H2),14,18 graphyne and 6BN,6,12 graphyne suggest that a wealth of two-dimensional materials with various chemical compositions and with electronic properties equally amazing as those of graphene is awaiting discovery.