Bandgap Nature Transition and the Optical Properties of ABX3 (A = K, Rb; B = Sr, Ba, Ca; X = Cl, Br, I) Perovskites under Pressure

The impact of induced pressure (0–20) GPa on the structural and optoelectronic properties of ABX₃ (A = K, Rb; B = Sr, Ba, Ca; X = Cl, Br, I) halide perovskites is investigated here using full-potential linearized augmented plane wave method within the density functional theory. The generalized gradient approximation is utilized to assess the exchange-correlation potential. Additionally, the optoelectronic characteristics of halide perovskite are studied using the modified Becke-Johnson for perovskite potential. There is a good agreement between the computed structural parameters and the existing data, including the bulk modulus, equilibrium lattice constant, total energy, and its pressure derivative. It has been determined from these computations that these materials have an indirect energy band gap (M − Γ) at 0 GPa. At pressures of 10 GPa, RbSrCl₃ and KBaCl₃, and 20 GPa RbSrCl₃, KBaCl₃, KSrBr₃, and RbSrBr₃ transform into direct band gaps due to the high pressure. For the energy range of 0–40 eV, the optical spectra are calculated, including the dielectric functions, extinction coefficient, electron energy loss, refractive index, optical conductivity, reflectivity, and absorption coefficient. Except for RbSrCl₃, the majority of the investigated attributes for these compounds under 0 and high pressure are reported for the first time. When the elastic characteristics of all cubic compounds are examined using the IRelast software, the results demonstrate the mechanical stability of these compounds. RbSrCl₃ and RbCaBr₃ show a more ductile nature at 0 GPa. While the Debye temperature values of all compounds increase with increasing pressure.