First-principles study on the electronic structure and optical properties of orthorhombic CaTiO3 under different pressures

The lattice constants, band structure, density of states (DOS), and optical properties of orthorhombic CaTiO3 in the pressure range of 0-100 GPa were calculated using the GGA-PBE method based on first -principles in this study. Geometry structure optimization results show that with an increase in pressure, the lattice constants of orthorhombic CaTiO3 decrease and the band gap (Eg) value increases. However, increasing pressure does not change the type of band gap in orthorhombic CaTiO3, which remains a direct band gap with the valence band maximum (VBM) and conduction band minimum (CBM) both located at the G point. The calculated electronic structure results indicate a gradual decrease in the DOS peak intensity for Ca-p, Ca-d, O-s, and O-p orbitals with increasing pressure, while the DOS peak intensity for the Ti atom remains relatively stable. Meanwhile, the valence band near the Fermi level shifts to the lower energies, while the conduction band shifts to the higher energies. Further calculations show that the optical properties exhibit a consistent blue shift as pressure increases. The research findings reveal that orthorhombic CaTiO3 demonstrates low absorption of visible light and high absorption of ultraviolet (UV) light. Moreover, as the pressure increases, the absorption of visible light further diminishes, while the absorption of UV light gradually intensifies. The findings presented in this paper offer significant insights for investigating the electronic structure and optical properties of orthorhombic CaTiO3 under varying pressure conditions.