Ground-state structure determination and mechanical properties of palladium seminitride

Combining first-principles calculations with the particle swarm optimization (PSO) algorithm, we have explored the ground-state structure of Pd₂N, whose structure is in debate although it is the first synthesized binary platinum group nitride. The ground-state structure is predicted to be tetragonal with space group P4m2, which is energetically more favorable than the previously proposed orthorhombic Co₂N-type structure. The stability is confirmed by the subsequent calculations on the phonon dispersion curves and elastic constants. Furthermore, the calculated mechanical properties indicate that Pd₂N has low incompressibility and is a common hard material.