High-pressure structure prediction and physical properties of MnN2: First-principles calculations

Manganese nitrides have attracted considerable research interest since their rich physical properties and important application prospects. By employing an evolutionary algorithm approach and first-principles calculations, the stable crystal structures of MnN2 in the pressure range of 0–200 GPa are systematically explored. Two novel high-pressure MnN2 phases, Pm and Cmc21, are predicted. The Pm phase is the most stable structure within the pressure range of 153.5–155.9 GPa, and it transforms into Cmc21 configuration at 155.9 GPa. By calculating the phonon spectra and molecular dynamics simulations, the dynamical stability and thermodynamic stability are examined. To uncover the potential applications of them, we investigate their mechanical properties and magnetism. Pm-MnN2, as a metal system, exhibits outstanding bulk modulus (296.1 GPa) and impressively high Vickers hardness (up to 30.5 GPa). Furthermore, the electronic mechanism underlying the excellent hardness of Pm-MnN2 is discussed by analyzing the crystal orbital Hamilton populations. Besides, Cmc21-MnN2 exhibits ferromagnetic configurations.