QHOD-Net: A New Highly Metallic Two-Dimensional Carbon Allotrope Material

We propose a new two-dimensional metallic carbon allotrope named QHOD-net using first-principles calculations, the structure of which includes five carbon rings; quadrangular, pentagonal, hexagonal, octagonal, and decagonal. This metastable phase metallic carbon material displays anisotropic mechanical properties, and its smallest and largest in-plane stiffness have been calculated to be C-a = 261 GPa nm and C-b = 240 GPa nm, respectively, both much lower than for graphene. The Poisson's ratio is as low as 0.29, which has good toughness. The DFT indicates that QHOD-net is metallic with no bandgap in the entire BZ region and one band crosses the Fermi level. At the Fermi level, the electron density of states per atom is much higher, reaching similar to 0.297 eV/states/per atom. In addition, we have performed the 3D stacked structure of the two-dimensional structure QHOD-net, and the results of our study indicate that the stacked structure is a super-hard 3D carbon material (74.8 GPa nm). The two-dimensional structure QHOD-net contains a large number of tetragonal, pentagonal, octagonal, and decagonal carbon rings than the perfect hexagonal shape of ideal graphene. The disorder of the material is increased compared to that of graphene. It is this disorder that triggers these interesting findings, and in addition we provide a new strategy for the design of 2D structures with multiple carbon rings.