First-principles investigations on mechanical stability and elastic properties of hexagonal tungsten dinitride under pressure

The first-principles study on the mechanical stability, elastic and thermodynamic properties of WN2 with P63/mmc and P-6m2 phases are reported using the pseudopotential plane wave method within the generalized gradient approximation. The calculated equilibrium parameters are in good agreement with the available theoretical data. A complete elastic tensor and crystal anisotropies of the ultra-incompressible WN2 are determined in the wide pressure range. By the elastic stability criteria, it is predicted that P63/mmc and P-6m2 phases in WN2 are not stable above 175.1 GPa and 170.1 GPa, respectively. Finally, by using the quasi-harmonic Debye model, the bulk modulus, relative volume, the coefficient of thermal expansion, and the Grüneisen parameter of WN2 are also successfully obtained in the present work.