IMF2017

In the present paper we haveinvestigated the electronic structure of some orthorhombicA₃X₂S₇(X = Ti, Zr, and Hf) compounds based on density functional theory. Then we extend the Ruddlesden-Popper(RP) A₃X₂S₇sulfides 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 such as Young's modulus, shear modulus, Poisson's ratio, anisotropy factor, sound velocities, Debye temperature, and hardness have also been estimated in the present work.The band gap trend in A₃X₂S₇ can be understood from the nature of their elec-tronic structures. The obtained electronic band structure for Ba₃Zr₂S₇and Ba₃Hf₂S₇compounds are semiconductor in nature, and the Ba₃Ti₂S₇ compound also is semi-metal. Similar to ferroelectric oxides, there are pronounced hy-bridization of electronic states between X-site cations and anions in A₃X₂S₇. Based on the obtained electronic struc-tures, we further calculate the frequency-dependent di-electric function and other optical functions in different phases.