Elastic Properties of Lithium and Sodium Amides

This paper presents the optimization of the structural parameters of tetragonal and orthorhombic crystals α-LiNH₂ and α-NaNH₂ and computation of elastic constants and flexibility coefficients using the all-electron implementation of the Gaussian and augmented plane wave density functional method. The obtained elastic constants satisfy all conditions of mechanical stability of LiNH₂ and α-NaNH₂ crystals. From the viewpoint of elastic properties, α-LiNH₂ crystal is isotropic, while α-NaNH₂ crystal is rather anisotropic. Anisotropy under compression in α-NaNH₂ crystal is higher than that under shear. The former is brittle, the latter is more plastic.