Mechanical stability of possible structures of PtN investigated using first-principles calculations

We report an ab initio study of the mechanical stability of platinum nitride (PtN), in four different crystal structures, the rock salt (rs-PtN), zinc-blende (zb-PtN), cooperite, and a face-centered orthorhombic phase. Of these phases only the rs-PtN phase is found to be stable and has the highest bulk modulus $B=284\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. Its electronic density of states shows no band gap making it metallic. The zb-PtN phase does not stabilize or harden by the nitrogen vacancies investigated in this study. Therefore, the experimental observation of super hardness in PtN remains a puzzle.