First principles study of structural, electronic and optical properties of polymorphic forms of Rb2Te

First-principles density functional theory calculations have been performed for structural, electronic and optical properties of three polymorphic forms of rubidium telluride. Our calculations show that the sequence of pressure induced phase transitions for Rb2Te is F m 3 A= m ANBaANBPnmaANBaANBP63/mmc which is governed by the coordination numbers of the anions. From our calculated low transition pressure value for the F m 3 A= m phase to the Pnma phase transition of Rb2Te, the experimentally observed meta-stability of F m 3 A= m phase at ambient conditions seems reasonable. The electronic band structure has been calculated for all the three phases and the change in the energy band gap is discussed for the transitioning phases. The energy band gaps obtained for the three phases of Rb2Te decrease on going from the meta-stable phase to the high-pressure phases. Total and partial density of states for the polymorphs of Rb2Te has been computed to elucidate the contribution of various atomic states on the electronic band structure. Furthermore, optical properties for all the polymorphic forms have been presented in form of the complex dielectric function. Anion coordination polyhedra of the three polymorphic forms of Rb2Te: