DFT analysis of wide band gap TlBaCl₃ and CsBaCl₃ chloroperovskites for UV applications

In this work, we investigate the structural, electronic, optical, and elastic properties of RBaCl₃ (R = Tl and Cs) chloroperovskites using Density Functional Theory (DFT). The Tran-Blaha modified Becke-Johnson (TB-mBJ) potential within the WIEN2k code is employed to enhance the accuracy of exchange-correlation effects. Structural optimization is performed by fitting the energy-volume data to the Birch-Murnaghan equation of state, yielding lattice constants, bulk modulus, equilibrium volume, ground-state energy, and the pressure derivative of the bulk modulus. The electronic properties, including the band structure and density of states (DOS), reveal that both TlBaCl₃ and CsBaCl₃ are insulators with indirect band gaps of 5.51 eV and 7.14 eV, respectively. DOS analysis indicates that the valence band is mainly composed of Ba and Cl states, while the conduction band is predominantly contributed by Tl and Cs. Elastic property calculations confirm the mechanical stability of both compounds. TlBaCl₃ is found to be more ductile and slightly more anisotropic, whereas CsBaCl₃ is stiffer, less ductile, and exhibits more isotropic elastic behavior. Optical properties, including the dielectric function, optical conductivity, reflectivity, refractive index, absorption coefficient, extinction coefficient, and energy loss function, are evaluated across the photon energy range of 0-14 eV. The results show strong optical activity in the ultraviolet (UV) region, suggesting that both compounds have excellent potential for optoelectronic applications. Due to their wide band gaps, mechanical robustness, and UV sensitivity, RBaCl₃ chloroperovskites are promising candidates for use in advanced electronic devices and scintillation-based radiation detectors.