First-principles prediction of the structural, elastic, electronic and optical properties of the Zintl phases MIn2P2 (M = Ca, Sr)

We have performed a detailed theoretical study of the structural, elastic, electronic and optical properties of two newly synthesized Zintl phases CaIn2P2 and SrIn2P2 by means of first-principles calculations based on density functional theory within the generalized gradient approximation of Wu and Cohen. The optimized lattice parameters, including the lattice constants and internal coordinates, are in good agreement with the existing experimental measurements. The relative changes of the structural parameters versus hydrostatic pressure have been investigated. The elastic properties of MIn2P2 have been examined by calculating all independent single-crystal elastic constants C-ij using the static finite strain technique, and the polycrystalline isotropic elastic moduli, namely bulk modulus, shear modulus, Young's modulus and Poisson's coefficient, via the Voigt-Reuss-Hill approximations. The elastic wave velocities along some crystalline directions have been evaluated. The mechanical stability of the considered materials has been examined on the light of the pressure dependence of the elastic constants. The elastic anisotropy of the two phases has been studied using three different methods. The electronic properties have been studied throughout the calculations of the band structure, density of states, charge density distributions, charge transfers, and charge-carries masses. These two materials turn out to be narrow gap semiconductors. Finally, we have predicted the basic optical properties, such as the dielectric function, refractive index, extinction coefficient, reflectivity coefficient, absorption coefficient and loss function for polarized incident radiation with electrical vector E parallel to the crystalline axes a and c. A considerable anisotropy is observed in the frequency dependent optical spectra. (C) 2013 Elsevier B.V. All rights reserved.