Revealing the remarkably improved structural, phonon, elastic, optoelectronic and thermoelectric properties of TlXF3(X = Ca, Cd) for energy applications using first-principles approach with hybrid and range-separated hybrid functionals

This study reports the first-principles investigations of flouroperovskites, TlXF₃(X $=$ Ca, Cd), within the frame work of Density Functional Theory. A comprehensive and improved data of flouroperovskites on structural, phonon, elasto-mechanical, optoelectronic and thermoelectric properties are carried out using Perdew Burke Ernzerhof-Generalized Gradient Approximation (PBE-GGA), Trans-Blaha modified Becke–Johnson (TB-mBJ), meta GGA, Strongly Constrained and Appropriately Normed (SCAN), hybrid functional including Becke’s three parameter exchange functional with the Lee–Yang–Parr (B3LYP) and range-separated hybrid functional Heyd–Scuseria–Ernzerhof (HSE06). The structures are optimized and stability is proved by energy-volume optimization, formation energy calculations, positive phonon frequencies of phonon dispersion curves and elastic constant criteria. The electronic band structures of both TlCaF₃ and TlCdF₃ possess direct and indirect nature respectively and density of states are consistent with electronic band structure. The band gaps of TlCaF₃ are 4.53 eV (PBE-GGA), 6.19 eV (TB-mBJ), 4.89 eV (SCAN), 6.24 eV (B3LYP) and 5.98 eV (HSE06) and the band gaps of TlCdF₃ are 3.74 eV (PBE-GGA), 5.64 eV (TB-mBJ), 4.30 eV (SCAN), 5.83 eV (B3LYP) and 5.53 eV (HSE06). The dynamical stability and brittle response of TlCaF₃ and TlCdF₃ is confirmed from shear constant, Pugh’s ratio and Poisson’s ratio. The optical and thermoelectric response are studied for optoelectronic and sustainable applications.