First‐Principles Calculations of Physical Properties and Stability of Orthorhombic FeN2 under High Pressure.

The physical properties and stability of orthorhombic FeN2 under high pressure remain an open question. The spin‐polarized first‐principles calculations within the generalized gradient approximation GGA + U functional are used to study the structural, elastic, electronic, magnetic properties and the stability of orthorhombic FeN2 under high pressure. The variations of the lattice constants and bond lengths as a function of pressure in the range 0–100 GPa are presented. The elastic constants, moduli, Poisson's ratio, elastic wave velocities, Debye temperature, and thermal expansion coefficient as a function of pressure in the range 0–100 GPa are also given. The high bulk modulus and low compression make it a promising high‐energy‐density material. FeN2 is both mechanically and dynamically stable in the studied pressure range. FeN2 is elastic anisotropic and its anisotropy increases with pressure. At pressure less than 45 GPa, the orthorhombic FeN2 is a magnetic metal, while at pressure increasing to 45 GPa, a nonmagnetic metal is obtained. When the pressure goes beyond 45 GPa, the outline of the density of states is similar, showing that the pressure has less effect on electronic properties. It is hoped that these results can provide reference for further researches. [ABSTRACT FROM AUTHOR]