  We report density functional theory calculations on the crystal structure,
elastic, lattice dynamics and electronic properties of iso-structural layered
monoclinic alkali azides, LiN3 and NaN3. The effect of van der Waals
interactions on the ground- state structural properties is studied by using
various dispersion corrected density functionals. Based on the equilibrium
crystal structure, the elastic constants, phonon dispersion and phonon density
of states of the compounds are calculated. The accurate energy band gaps are
obtained by using the recently developed Tran Blaha-modified Becke Johnson
(TB-mBJ) functional and found that both the azides are direct band gap
insulators.
