Electronic, mechanical, and optical properties of Ruddlesden-Popper perovskite sulfides: First principle calculation

In the present paper we have investigated the electronic structure of some orthorhombic A(3)X(2)S(7) (X = Ti, Zr, and Hf) compounds based on the density functional theory. Then we extend the RuddlesdenPopper (RP) A(3)X(2)S(7) sulfides and examine how ferroelectricity is induced by coupled octahedral rotation modes. The mechanical and optical properties have also been computed. The second-order elastic constants have been calculated, and the other related quantities have also been estimated in the present work. The band gap trend in A(3)X(2)S(7) can be understood from the nature of their electronic structures. The obtained electronic band structure for Ba3Hf2S7 and Ba3Hf2S7 compounds are semiconductor in nature, and the Ba3Hf2S7 compound is also semi-metal. Similar to ferroelectric oxides, there is a pronounced hybridization of electronic states between X-site cations and anions in A(3)X(2)S(7). Based on the obtained electronic structures, we further calculate the frequency-dependent dielectric function and other optical functions in different phases.