Structural, electronic, optical, and thermoelectric properties of CaXO₃ (X = Si, Ge, Ti) perovskite for photovoltaics and optical devices.

We report a detailed first-principles investigation of the structural, electronic, optical, and thermoelectric properties of CaXO₃ (X = Si, Ge, Ti) perovskites using density functional theory with both GGA and mBJ-GGA functionals. Optimized lattice constants CaSiO₃ (3.6073 Å), CaGeO₃ (3.7775 Å), CaTiO₃ (3.8811 Å) reflect systematic variation with B-site cation size. Energy-volume optimization confirms structural stability, while phonon dispersions show no imaginary frequencies, indicating dynamical stability. All compounds are indirect-gap semiconductors, with band gaps strongly dependent on the computational method. Optical absorption edges span the UV to near-visible range, suggesting promise for optoelectronic and photovoltaic applications. Thermoelectric transport analysis at 400 K reveals favorable Seebeck coefficients and electrical conductivity profiles. Electron density difference mapping for CaGeO₃ highlights mixed ionic-covalent bonding in Ge-O linkages and primarily ionic Ca-O interactions. These integrated findings demonstrate the tunable potential of CaXO₃ perovskites for energy conversion and advanced optical devices.