Elastic stability and electronic structure of low energy tetragonal and monoclinic PdN₂ and PtN₂

This paper studies the elastic and electronic structure properties of two new low-energy structures of PdN₂ and PtN₂ by first-principles calculations. It finds that tetragonal and monoclinic structures are more stable than a pyrite one. The always positive eigenvalues of the elastic constant matrix confirm that both the tetragonal and monoclinic structures are elastically stable. The origin of the low bulk modulus of the two structures is discussed. The results of the calculated density of states show that both of the two low-energy structures are metallic.