First-principles calculations based on density functional theory (DFT) were employed to investigate the structural, electronic, and magnetic properties of pristine and single Fe-doped Al2Si2O5(OH)4 (kaolinite). All calculations were performed within the GGA–PBE framework using a plane-wave pseudopotential approach. Convergence tests with respect to kinetic energy cut-off and k-point sampling confirmed that 40 Ry and a 5×5×5 Monkhorst–Pack grid ensure total energy convergence within 1 meV/atom for both systems. Structural optimization of pristine kaolinite reproduces the characteristic layered framework of SiO4 tetrahedra and AlO6 octahedra. Upon Fe substitution at an octahedral Al site, localized structural relaxation is observed, with elongated Fe–O bonds (?1.95–2.12 Å), minor lattice expansion (