Ab initio study of the structural stability, elastic, electronic and optical properties of NaMgHiFj [(i, j) = (3, 0), (2, 1), (1, 2), (0, 3)] compounds

We studied the structural, elastic, electronic and optical properties of the orthorhombic NaMgH3, NaMgH2F, NaMgHF2 and NaMgF3 compounds. By means of the self-consistent CASTEP code, pseudopotentials, density functional theory in the LDA and GGA approximations, basic physical properties, such as lattice constant, shear modulus, elastic constants (Cij) and optical constants are computed. This study includes elastic parameters of mono and poly-crystalline aggregates. Derived elastic constants, such as bulk, Young's and Shear modulus, Poisson coefficient, Debye temperature and brittle/ductile behavior are estimated with the polycrystalline approach, using Voigt-Reuss-Hill theory. The calculations show that the orthorhombic Pnma structures are mechanically and dynamically stable in the pressure range (0-20 GPa). The calculated density of states shows that the orthorhombic compounds are insulators.