High pressure structural phase transition and optical properties of rubidium iodide (RbI)

The high pressure structural phase transitions, structural stability, and optical properties of rubidium iodide (RbI) were investigated in five different crystal structures using the Full-Potential Linearized Augmented Plane Waves (FP-LAPW) method in the framework of Density Functional Theory (DFT). The structures studied were Rock Salt (RS), Cesium Chloride (CsCl), Zincblende (ZB), Nickel Arsenide (NiAs), and Wurtzite (WZ). GGA-PBESOL functional approximation was employed to investigate the structural properties of the compounds while TB-mBJ was used to calculate various optical functions of the compounds, namely, the refractive index, reflectivity, electron energy loss, absorption coefficient, and the real and imaginary part of the dielectric functions. Our new calculations of the structural parameters and transition pressure show a good agreement with the experimental and other theoretical values. To our knowledge, this is the first systematic DFT study that simultaneously investigates the high-pressure phase transitions and optical properties of RbI across five crystal structures. Moreover, we note that RbI in all its studied structures possesses some potential optical applicability from the IR to early UV region, especially in the CsCl structure.