Theoretical calculations for structural, elastic, and thermodynamic properties of RuN2 under high pressure

The structural and elastic properties of RuN2 were investigated through the first-principles calculation using generalized gradient approximation (GGA) and local density approximation (LDA) within the plane-wave pseudopotential density functional theory. The obtained equilibrium structure and mechanical properties are in excellent agreement with other theoretical results. Then we compared the elastic modulus of RuN2 with several other isomorphic noble metal nitrides. Results show that RuN2 can nearly rival with OsN2 and IrN2, which indicate RuN2 is a potentially ultra-incompressible and hard material. By the elastic stability criteria, it is predicted that RuN2 is stable in our calculations (0–100 GPa). The calculated B/G ratios indicate that RuN2 possesses brittle nature at 0 GPa and when the pressure increases to 13.4 GPa (for LDA) or 20.8 GPa (for GGA), it begins to prone to ductility. Through the quasi-harmonic Debye model, we also investigated the thermodynamic properties of RuN2