Structural, electronic and mechanical properties of ReN2 from first principles

First principles calculations were performed to study the structural, electronic and mechanical properties of hypothetical rhenium dinitride ReN2 for various space groups. It was found that cubic Fm-3m and Pa-3, tetragonal P42/mnm, and orthorhombic Pmmn structures are mechanically stable and metallic. P42/mnm structure is thermodynamically stable at ambient conditions and up to 76 GPa. It has the shortest Re–N bond (1.964 Å). Compared with the considered structures, only Pmmn structure contains the diatomic N–N unit with the bond distance 1.502 Å and has the largest bulk modulus (371 GPa) and shear modulus (240 GPa). It becomes more stable than its constituents at 18 GPa and the most stable among the structures considered in this work above 76 GPa.