Structural, elastic, electronic and optical properties of KAlQ2 (Q = Se, Te): A DFT study

• Some physical properties of the layered semiconductor KAlQ2 have been predicted.
• Elastic parameters reveal that KAlQ2 are mechanically stable but with considerable anisotropy.
• KAlQ2 are found to be a direct band gap semiconductor.
• The optical spectra exhibit a noticeable anisotropy.

First-principles calculations in the framework of density functional theory have been conducted to explore the structural, elastic, electronic and optical properties of two layered ternary compounds chalcogenides of aluminum KAlSe2 and KAlTe2. We have calculated all of the equilibrium structural parameters; the lattice parameters (a, b and c), angle β and twenty three internal atomic coordinates. The obtained results are in excellent agreement with the available experimental data. We have predicted the single-crystal elastic constants Cij of the title materials using stress-strain approach and then derived the elastic moduli of the polycrystalline aggregates and related properties via the Voigt-Reuss-Hill approximations. The band structure and density of states diagrams have been calculated and analyzed. Both compounds demonstrate semiconducting behavior with direct band gap. The linear optical properties, namely the frequency-dependent dielectric function, absorption coefficient, refractive index, extinction coefficient, reflectivity and energy-loss function, have been calculated and analyzed in a wide energy range up to 20 eV.

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