Theoretical insights into the structures and fundamental properties of pnictogen nitrides

Recent experimental advancements reported a chemical reaction between antimony and nitrogen under high temperature and high pressure, yielding crystalline antimony nitride (Sb₃N₅) with an orthorhombic structure. Motivated by this statement, we calculate the stability, elastic properties, electronic properties and energy density of the Cmc2₁ structure for pnictogen nitrides X₃N₅ (X = P, As, Sb, and Bi) using first-principles calculations combined with particle swarm optimization algorithms. Calculations of formation enthalpies, elastic constants and phonon spectra show that P₃N₅, As₃N₅ and Sb₃N₅ are thermodynamically, mechanically and kinetically stable at 35 GPa, whereas Bi₃N₅ is mechanically and kinetically stable but thermodynamically unstable. The computed electronic density of states shows strong covalent bonding between the N atoms and the phosphorus group atoms in the four compounds, confirmed by the calculated electronic localization function. We also calculate the energy densities for Sb₃N₅ and find it to be a potentially high-energy-density material.