First-principles study of hydrogen vacancies in lithium amide doped with titanium and niobium

The crystal and electronic structures, the formation energy of H vacancies, and the diffusion path of the H atom (i.e., diffusion path of H vacancy) in unsubstituted and substituted LiNH2 crystal were investigated by periodic first-principles calculations. The bonding characters between atoms were studied by topological analysis of electron density. Our calculations reveal that substitution of the Li atom with Ti or Nb favors the formation of hydrogen vacancies adjacent to substitution, and the existence of an H vacancy and Ti or Nb substitution can cause weakening of nearby N–H bonds, which facilitates N–H bond dissociation. The minimum energy paths of H diffusion show that the substitution can reduce the energy barrier and thus favor H diffusion in the bulk phase of LiNH2.