First-principles study of structural, electronic, elastic, and optical properties of the tetragonal AInS₂ (A=K, Rb, Cs) chalcogenides

The structural, phonon, electronic, elastic, and optical properties of AInS₂ (A = K, Rb, Cs) compounds in the tetragonal phase were investigated using plane-wave pseudo potential method which is implemented in CASTEP code in the framework of density functional theory. The calculated cohesive energy indicates that all studied structures are chemically stable and thus, the predicted CsInS₂ tetragonal phase could be synthesized. The results show that KInS₂ is the most stable compound compared to RbInS₂ and CsInS₂ crystals. The pressure-induced phase transition from monoclinic to tetragonal phase of the studied structures was calculated. The physical parameters, such as lattice parameters, elastic moduli and their related properties for single-crystal and polycrystalline aggregates were predicted for the first time. The elastic and dynamical stability were confirmed by Born criteria and phonon spectra, respectively. The band structure of all the compounds reveal a semiconductor behavior. Finally, the optical properties were calculated and analyzed for incident radiation in the energy range 0–15 eV.