Theoretical investigation of the structural, electronic, elastic and optical properties of the ternary monoclinic compounds KGaQ2 (Q = S, Se and Te)

In this work we have carried out a theoretical study of structural, electronic, elastic and optical properties for the three ternary compounds KGaS2, KGaSe2 and KGaTe2, using the pseudo-potential plane-wave scheme in the framework of the density functional theory. The obtained structural parameters are very close to the available experimental data. The analysis of band structure indicates semiconducting behaviour of these compounds with a direct bandgap. The mechanical properties of the considered KGaQ2 are investigated by predicting the single-crystal elastic constants and the macroscopic elastic parameters, such as the bulk modulus and shear modulus. Our results indicate that all the compounds are mechanically stable and both KGaSe2 and KGaTe2 exhibit a significant elastic anisotropy compared to KGaS2 compound. A set of frequency dependent optical parameters were calculated for incident radiation polarized in the [100], [010] and [001] crystallographic directions, including the complex dielectric function, the refractive index and the absorption coefficient. The studied materials show anisotropic in the optical properties, especially in the real and imaginary part of the dielectric function and in the refraction index. In addition, the obtained results show that our compounds absorb in the UV region.