Novel high-pressure phase with pseudo-benzene “N₆” molecule of LiN₃

Abstract

The pressure-induced formation of a hexagonal phase (P6/m, Z = 2) of LiN3 is predicted by particle swarm optimization (PSO) structural search at zero temperature and pressure of > 34.7 GPa. Compared to the ground-state insulator C2/m phase, the P6/m-LiN3 is found to possess a metallic feature dominated by the 2pz bands. Electron topological analysis revealed an intriguing phase change of nitrogen, from azide to novel pseudo-benzene "N6" molecules at the formation of the P6/m phase. The occurrence of this hexagonal phase follows the polymerization of the typical linear N3− anion molecular chains in the low-pressure molecular phases of LiN3 and is originated from the volume reduction favorable for a denser structure packing under compression.