A first-principles study of the structural, elastic, electronic, vibrational, and optical properties of BaSe_1−xTe_x

The structural, elastic, electronic, vibrational, and optical properties of BaSe_1−xTe_x alloys are investigated by means of the full-potential linearized augmented plane wave method. The exchange–correlation effects are treated with the local density approximation, as well as the GGA-PBE, GGA-PBEsol, and GGA + mBJ schemes of the generalized gradient approximation. Ternary BaSe_1−xTe_x compounds have not yet been synthesized. Improved predictions of the structural parameters are obtained using the GGA-PBEsol approach. Calculations of the electronic and optical properties with the GGA + mBJ approach yield accurate results. Ternary BaSe_1−xTe_x alloys are wide-band-gap semiconductors with a direct gap Γ–Γ. The upper valence band is mainly due to Se p and Te p states, while the bottom of the conduction band results essentially from Ba d states. The dielectric function, refractive index, reflectivity, absorption coefficient, and energy-loss function are calculated in the range 0–35 eV. The increase in x gives rise to a redshift of the optical spectra. BaSe_1−xTe_x alloys exhibit reflective properties of metals in some energy ranges. The static dielectric constant ɛ₁(0) and the static refractive index n₀ are calculated. The investigation of the elastic and vibrational properties shows that ternary BaSe_1−xTe_x should be mechanically and dynamically stable, elastically anisotropic, brittle, and relatively soft.