A first-principles study of the structural, elastic, electronic, vibrational, and optical properties of BaSe1-xTex

The structural, elastic, electronic, vibrational, and optical properties of BaSe1-xTex 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 BaSe1-xTex 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 BaSe1-xTex alloys are wide-band-gap semiconductors with a direct gap Gamma-Gamma. 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. BaSe1-xTex alloys exhibit reflective properties of metals in some energy ranges. The static dielectric constant epsilon(1)(0) and the static refractive index n(0) are calculated. The investigation of the elastic and vibrational properties shows that ternary BaSe1-xTex should be mechanically and dynamically stable, elastically anisotropic, brittle, and relatively soft.