Novel nitrogen-rich lanthanum nitrides induced by the ligand effect under pressure

N-rich La-N compounds have been studied by first-principles calculations in this work. We identified nine unknown polynitrides, which reveals that the miraculous ligand effect of La plays an important role in the electronic properties and hybridization of nitrogen atoms. Unique tri-coordination atoms with alternate sp² and sp³ hybridizations are formed in the N₁₈ ring of LaN₈. The ligand effect of La induces a novel 1-D chain-like N₁₀ cage polymeric structure in LaN₁₀ and stabilizes it under mild pressure (25 GPa). Moreover, the ligand effect of the introduced La atom on the N₁₀ cage has been clarified by the analysis of the structural evolution behavior from I4̄3m-N₁₀ to Imm2-LaN₁₀. In addition, Imm2-LaN₁₀ with excellent energy (4.56 kJ g^-1) and explosive performance (V_d = 16.88 km s^-1, V_p = 1887.53 kbar) is a good energetic material candidate.