Structure, bandgap and optical properties of cubic CsPbX3 halides (X = Cl, Br and I) under hydrostatic pressure

In the recent years, caesium lead halides CsPbX 3 with the halogen elements Cl, Br and I have gained much attention of researchers owing to their attractive optical properties.In the present work we discuss the changes in their structure, bandgap and optical properties that occur under hydrostatic pressures 1-10 GPa.The density functional theory based on the generalized gradient approximation within the Perdew-Burke-Ernzerhof approach for exchange-correlation energy is used for calculations, in conjunction with the augmented plane-wave pseudopotential method.Since the generalized gradient approximation underestimates the bandgap, we employ the GW method to improve the bandgap values.The optical properties are computed in the photon-energy range 0.1-3.6 eV, using the density functional perturbation theory.As the pressure increases, the Pb-halogen bonds become contracted, whereas the volume of the unit cell shrinks uniformly, with no phase or structure-type transformations.The bandgap decreases with increasing pressure and the corresponding decrease rate for CsPbI 3 is less than that for CsPbBr 3 .In general, the optical response of the caesium lead halides increases with increasing pressure, while the peaks of maximums of the response functions are red-shifted.