Density functional theory First-principles Electronic structure Electronic structure and optical properties Energy gap Generalized gradient approximations Optical properties Absorption spectroscopy Band structure Ca-doped α-Ga2O3 Calcium Calculated optical properties Calculations Carbon Charge density distributions Chemical bonds Complex dielectric functions Corrosion Crystal structure Date palm seed (DPS) extract Density functional theory (DFT) Density of states Electrical and optical properties Exchange-correlation potential First-principles calculation First-principles study Gallium compounds Green anti-corrosive HCl High-power transistors