Native defects in LiNH₂: A first-principles study

Native defects in lithium amide (LiNH₂), a promising candidate for hydrogen storage, are investigated by first-principles calculations based on density functional theory. We examine the structural properties and formation energies of H-, Li-, and N-related defects in all possible states. We find that the dominant H- and Li-related defects are in charged states, i.e., negatively charged H vacancy (V_H^-), positively charged H interstitial (H_i⁺), negatively charged Li vacancy (V_Li ^-), and positively charged Li interstitial (I_Li ⁺). V_Li^- and I_Li⁺ are present in the highest concentration. The positively charged NH₂ vacancy has the lowest formation energy among N-related defects. Furthermore, migration processes of the dominant defects are investigated. V _Li^- diffuses most rapidly with the lowest migration energy of 0.20 eV. Both formation and migration energies of Li-related dominant defects are found to be lower than those of H-related dominant defects. With an activation energy of 0.72 eV, V_Li^- is the major diffusive species in LiNH₂. Our results further indicate that the formation of H_i is the bottleneck for H transport.