Alkaline Earth Metal Doping Effects on the Electronic and Optical Properties of Iron Sulphide: a DFT Study

We report a systematic DFT study of pristine and alkaline earth metal (AEM: Be, Mg, Ca, Sr, Ba)–doped FeS, focusing on structural, electronic, and optical properties. The calculations were performed using the CASTEP code within DFT, employing a plane-wave cutoff energy of 550 eV for numerical convergence. Substitutional doping induces slight lattice expansion and modifies the electronic structure, with Fe 3d orbitals dominating states near the Fermi level. Calculated band gaps range from 0.34 to 1.57 eV, showing tunability depending on the dopant type. Optical spectra reveal strong absorption in the ultraviolet region (≈10–20 eV), with a weak low-energy tail near the band edge; no significant visible-light absorption is predicted. High refractive indices (n > 3) indicate strong electronic polarizability, while large extinction coefficients (k) correspond to efficient UV absorption. The results highlight how AEM doping can tune electronic and optical behavior, providing insights for future experimental studies and potential applications in UV photonics and optoelectronic devices.