Structural, elastic, electronic, chemical bonding and thermodynamic properties of CaMg2N2 and SrMg2N2: First-principles calculations

We report first-principles density functional theory calculations of the structural, elastic, electronic, chemical bonding and thermodynamic properties of the ternary alkaline earth metal nitrides CaMg2N2 and SrMg2N2. The calculated equilibrium structural parameters agree well with the experimental findings. Single-crystal and polycrystalline elastic constants and some related properties under pressure effect have been predicted. Both compounds exhibit a striking elastic anisotropy and a ductile behavior. Electronic properties and chemical bonding nature have been studied throughout the band structure, density of states and charge distribution analyses. It is found that these two materials have a direct band gap (Γ–Γ) and a transition to an indirect gap (Γ–M) occurs at about 8.63 and 5.16 GPa in CaMg2N2 and SrMg2N2, respectively. The chemical bonding has a mixture covalent-ionic character. Thermal effects on some macroscopic properties are predicted using the quasi-harmonic Debye model.