A First-Principles Calculation of Electronic Properties of LiNH2 and NaNH2

Band spectra, densities of states, total and deformation densities of α-LiNH2 and α-NaNH2 are calculated from the first principles using the density functional method in the all-electron approximation. The upper valence band is formed mostly by nitrogen p-states with a small admixture of metal states, the lower conduction bands are formed by the states of all atoms in α-LiNH2 and mainly by sodium and nitrogen states in α-NaNH2. The bottom of the conduction band appears in both crystals in the center of the Brillouin zone. α-LiNH2 exhibits indirect-gap transitions at the absorption edge and three valence band extrema at a short distance of ~0.15 eV from each other. The top of the valence band in α-NaNH2 appears in the center of the Brillouin zone with the competing maximum at the lateral point at a distance of ~0.06 eV. The electron density distributions testify that polar covalent bonding occur inside the amide anion and ionic bonding occurs between the metal and the amide ion.