Novel high-pressure phase with pseudo-benzene “N 6 ” molecule of LiN 3

The pressure-induced formation of a hexagonal phase ( P 6 /m , Z = 2) of LiN 3 is predicted by particle swarm optimization (PSO) structural search at zero temperature and pressure of > 34.7 GPa. Compared to the ground-state insulator C 2 /m phase, the P 6 /m -LiN 3 is found to possess a metallic feature dominated by the 2 p z bands. Electron topological analysis revealed an intriguing phase change of nitrogen, from azide to novel pseudo-benzene “N 6 ” molecules at the formation of the P 6/ m phase. The occurrence of this hexagonal phase follows the polymerization of the typical linear N 3 − anion molecular chains in the low-pressure molecular phases of LiN 3 and is originated from the volume reduction favorable for a denser structure packing under compression.