Ab initio study of monoclinic iridium nitride as a high bulk modulus compound

The first-principles calculations were performed for various structures of IrN2 as candidates of the new phase which was recently synthesized under high pressure. It was found that the monoclinic structure is the most stable and shows higher bulk modulus than pyrite PtN2. The simulated x-ray diffraction pattern agrees well with the experimental one. The positive formation energy of monoclinic IrN2 indicates that high-pressure is a necessary condition for synthesizing it. The band structure shows that monoclinic IrN2 is an insulator. The insulating behavior is mainly due to the dimerization of the Ir atoms, which lifts antibonding states formed by Ir d orbitals.