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 Pt N2, Os N2, and Os O2 are mechanically stable. In particular, Os N2 has the highest bulk modulus of 360.7 GPa. Both the band structure and density of states show that the new phase of Os N2 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.