Structural stability, electronic structure and mechanical properties of Li-N-H system

Abstract

Ab initio calculations are performed to investigate the ground state properties, structural phase transition, electronic structure and mechanical properties of lithium nitride (Li3N), lithium imide (Li2NH) and lithium amide (LiNH2). The computed ground state properties like equilibrium lattice constant, cell volume, valence electron density, cohesive energy, bulk modulus and its derivatives are in good agreement with available experimental data. The structural phase transitions from α-P6/mmm to β-P63/mmc phase at a pressure of 17.5 GPa in Li3N and cubic (Fm3m) to hexagonal (P63/mmc) phase at a pressure of 102 GPa in lithium imide (Li2NH) are observed. A new high pressure hexagonal (P63/mmc) phase is predicted for Li2NH. Electronic structure reveals that Li3N and LiNH2 are semiconductors, whereas Li2NH is an insulator. The calculated elastic constants indicate that these materials are mechanically stable at ambient condition.