Potential superhard osmium dinitride with fluorite and pyrite structure: First-principles calculations

We have performed systematic first-principles calculations on dicarbide, -nitride, -oxide, and -boride of platinum and osmium with the fluorite structure. It is found that only PtN₂, OsN₂, and OsO₂ are mechanically stable. In particular, OsN₂ has the highest bulk modulus of 360.70.3em0exGPa. Both the band structure and density of states show that the new phase of OsN₂ is metallic. The high bulk modulus is owing to the strong covalent bonding between Os $5d$ and N $2p$ states and the dense packed fluorite structure. In addition, the total-energy calculation for pyrite structure has also been performed, which indicates its mechanical and energetic stability but much lower bulk modulus compared to the fluorite structure.