Ab initio study of the lattice dynamical and thermodynamic properties of SbXI (X= S, Se, Te) compounds

The Born effective charges, high-frequency dielectrics constants, vibrational and thermodynamics properties of paraelectric SbSeI, SbTeI, SbSI and ferroelectric SbSI phase have been calculated by ab-initio method within the local density approximation. The high-frequency dielectric and Born effective charge tensor components are analyzed within density functional perturbation theory. We find remarkably enhanced/reduced Born effective charges and anomalously high-frequency dielectric constants for SbXI compounds. The phonon dispersion spectra and density of phonon states of these compounds were acquired using the direct method based on calculated Hellmann-Feynman forces. A comparison with the phonon dispersion curves of SbXI compounds displays minor differences that can attributed to the atomic-mass difference among S, Se and Te. The Raman and infrared active phonon mode frequencies of compounds are predicted at the Γ point. The thermodynamic properties of these compounds such as the internal energy, Helmholtz free energy, entropy, heat capacity, and Debye temperature are also investigated and discussed in the framework of the harmonic approximation. The obtained results were compared with available experimental and other theoretical data.