Investigation of structural, dynamic and thermodynamic properties of SbXI (X=S,Se,Te) compounds with AB initio method

In this work, the structural, electronic, elastic, Born effective charges, dielectrics, thermodynamic, vibrational properties of orthorhombic SbX(= S, Se, Te)I compounds were calculated using the LDA and GGA approximation with density functional theory based on ab initio method. Energy band structures show that SbXI compounds have an indirect band gap. Electronic charge distributions of SbXI compounds suggest that the Sb–X and Sb–I bonds are covalent–ionic type. Born effective charges, dielectric permittivity tensors and elastic properties have been calculated within the framework of density functional perturbation theory. The calculated independent elastic constants indicate that SbXI compounds are mechanically stable. Some fundamental physical quantities such as bulk modulus, shear modulus, sound velocity, Young's modulus, Poisson's ratio, crystal anisotropy and Debye temperatures of these compounds were derived from computed data. The density of phonon states and phonon dispersion curves of SbXI were obtained using the direct method based on computed Hellmann–Feynman forces. The infrared and Raman active phonon mode frequencies at the Γ point are found. The thermodynamic properties of SbXI crystals such as the Helmholtz free energy, internal energy, heat capacity and entropy are also investigated using the harmonic approximation. The obtained results were compared with the existing experimental and other theoretical data.