Pressure-dependent structural, electronic, optical, and mechanical properties of cubic PbTiO₃ perovskite: A DFT–GGA study

In this study, the structural, electronic, optical, and mechanical properties of cubic PbTiO₃ perovskite were systematically investigated using first-principles calculations based on density functional theory (DFT) within the generalized gradient approximation using the PBE functional. The calculations were performed with CASTEP. The optimized lattice parameter of the cubic phase is 3.96 Å, in good agreement with reported experimental and theoretical values. The electronic band structure indicates semiconducting behavior with an indirect GGA-PBE band gap of 1.70 eV. The upper valence band is dominated mainly by O-2p states with minor Pb-6p contributions, whereas the lower conduction band is dominated by Ti-3d states, confirming strong Ti-O hybridization. The optical response, derived from the complex dielectric function, shows strong activity in the ultraviolet region, with prominent absorption features near 3.89 and 6.78 eV. The calculated static dielectric constant and refractive index are 8.74 and 2.99, respectively. The optical conductivity exhibits a main peak at approximately 11.2 eV at ambient pressure. Under hydrostatic pressure from 0 to 50 GPa, the lattice parameter decreases monotonically, while the bulk modulus increases from 115 to about 298 GPa. In addition, the energy-loss function shows a pressure-induced blue shift of the plasmon peak from 11.02 to 13.01 eV. The novelty of this work is the unified analysis of the coupled pressure-dependent structural, electronic, optical, and mechanical properties of cubic PbTiO₃ up to 50 GPa within a single GGA-PBE framework. These results provide theoretical insight into the pressure-tunable behavior of PbTiO₃ and indicate its potential relevance for ultraviolet optoelectronic and high-pressure functional applications.