Nitrogen–hydrogen, carbon monoxide, phosphorus, and iron extended solids under pressure: Beyond pentazole, chain and molecular structures

Structures of H-N, CO–N 2 , P–N, and Fe–N solids under high pressure are studied using evolutionary algorithms and DFT calculations of phonon dispersion and elastic constants. Thermodynamically and dynamically stable structures are complemented by estimates of mechanical stability in elastic limit according to Born conditions. We focus on the structures with three-dimensional covalent bonds. The HN 4 structure with the Pbam symmetry group at 50 GPa is bound to be mechanically stable. The structures of CON 2 crystal with P4 3 symmetry at 40 GPa is mechanically stable. P 3 N 5 with Imm2 symmetry group and P 3 N 4 with C2/m symmetry are found to be dynamically and mechanically stable at 50 GPa. The predicted structures of iron–nitrogen compounds FeN with P6 3 symmetry and FeN 2 with Pnnm symmetry are found to be thermodynamically, dynamically, and mechanically stable. The predicted structures of CON 2 and Fe–N are in good agreement with the experimental determination of the symmetry based on single-crystal X-ray diffraction. Graphical abstract