Crystal, electronic structure and stability of LiNH₂-X (X＝Mg, Al, Ti, Nb) system have been determined from first-principles calculation based on the density functional theory. The calculated negative heat of formation and dissociation energy of H atom show that when a little X dissolve into LiNH₂ in a small amount of replacement solution, there are some changes on structural stability, alloying elements benefit to improve the dehydrogenating properties of the system and Nb was considered as the best element. Some results from theoretical calculation which alloying system can improve the dehydrogenation properties of LiNH₂ hydride are in agreement well with other ones. After comparing the densities of states (DOS) and the charge distribution, it is found that the catalysis effect of X (X＝Mg, Al, Ti, Nb) on dehydrogenating kinetics of LiNH₂ may attribute to the changes of energy gap near the Fermi level and the weakened bonding between Li and NH.

Key words: plane-wave pseudopotential theory, LiNH₂, heat of formation, electronic structure