Structural properties of a hypothetical H6-Boron with three-dimensional all sp2 network

New H6-Boron (H6-B) is predicted by first-principles calculations of density-functional theory. The proposed boron crystal is a rigid three-dimensional network with covalent sp2 coordination only and short interatomic distance 1.605 Å. Our results show that the novel form of pure boron holds a bulk modulus of 148 GPa and an estimated high hardness of 51 GPa, and it is also metallic without doping with other elements. The cohesive energy is calculated as 6.34 eV/atom, comparable with other boron polymorphs, which indicates that H6-B could be thermodynamically stable at ambient pressure. These results speculate that H6-B is a potential candidate of all sp2 covalent crystal.