Interstitial dinitrogen makesPtN2an insulating hard solid

Recent synthesis of platinum nitride has provoked considerable interest on account of the compound's anomalously high bulk modulus, which is more than 30% higher than that of the parent metal. Numerous theoretical studies have since offered contradicting hypotheses on the structure and properties of this com- pound. Here we show, based on first-principles calculations, that the recently synthesized phase of platinum nitride has the pyrite structure. In the PtN2 pyrite structure single-bonded N2 units occupy the octahedral interstitial sites of the Pt close-packed lattice, giving rise to strong, directional Pt-N bonds and to an insulating character. Excellent agreement with x-ray, Raman, and compressibility measurements is obtained