First-principles investigation of pressure-induced bandgap tuning of lead-free ASiF 3 (A=Na, K, Rb) Fluoroperovskites

First-principles calculations were performed to investigate the pressure-dependent structural, electronic, mechanical, optical, and thermal properties of ASiF 3 ([Formula: see text], K, Rb) fluoroperovskites from 0 to 12 GPa using DFT within the GGA-PBE functional. Band-structure analysis shows that NaSiF 3 , KSiF 3 , and RbSiF 3 are direct bandgap semiconductors at ambient pressure, with GGA-PBE bandgaps of 0.609, 0.805, and 0.918[Formula: see text]eV, respectively. The bandgaps decrease strongly under compression, and additional GGA[Formula: see text]U and HSE06 calculations confirm pressure-induced bandgap narrowing. Within HSE06, the bandgaps decreased from 1.198, 1.730, and 1.782[Formula: see text]eV at 0[Formula: see text]GPa to 0, 0.642, and 0.671[Formula: see text]eV at 12[Formula: see text]GPa for NaSiF 3 , KSiF 3 , and RbSiF 3 , respectively. Lattice parameters and bond lengths reduce at higher pressures, confirming lattice compression while preserving the cubic crystal framework. Optical conductivity and absorption are improved with a red shift to lower photon energies under pressure, indicating a pressure-tunable optical response. Mechanical analysis indicates anisotropic and ductile behavior, with KSiF 3 and RbSiF 3 showing better stability under compression than NaSiF 3 . Thermal analysis shows pressure-dependent Debye temperature, melting temperature, and lattice thermal conductivity. These results indicate the possible relevance of lead-free ASiF 3 fluoroperovskites for pressure-tunable optoelectronic and ultraviolet photonic applications.