Potential super-hard Osmium di-nitride with fluorite structure: First-principles calculations

We have performed systematic first-principles calculations on di-carbide, -nitride, -oxide and -boride of platinum and osmium with the fluorite structure. It is found that only PtN${}_2$, OsN${}_2$ and OsO${}_2$ are mechanically stable. In particular OsN${}_2$ has the highest bulk modulus of 360.7 GPa. Both the band structure and density of states show that the new phase of OsN${}_2$ is metallic. The high bulk modulus is owing to the strong covalent bonding between Os 5$\mathit{\text{d}}$ and N 2$\mathit{\text{p}}$ states and the dense packed fluorite structure.