A novel layer-structured PtN₂: First-principles calculations

The potential structures of platinum nitride with a chemical composition of PtN2 have been examined by utilizing a widely adopted evolutionary methodology for crystal structure prediction. Except reproducing the previously proposed phases, a Pmmm symmetric novel layer structure with a low formation enthalpy that is slightly lower than those of marcasite and CoSb2 structures but slightly higher than that of pyrite structure has also been identified. The elastic constants and the lattice dynamical calculations show that this layer-structured PtN2 is mechanically and dynamically stable. The calculated band structures suggest this new phase together with the simple tetragonal phase are metallic, while other phases are insulators. In addition, it has been found by the phonon spectrum calculations that the fluorite structure is dynamically unstable, although it is mechanically stable as suggested by calculated elastic constants.