First‐Principles Design of Cubic Spinel ZnIn ₂ S ₄ With Enhanced Carrier Transport, Optical Response, and Mechanical Stability for Photocatalytic an

ZnIn ₂ S ₄ is a ternary sulfide semiconductor that has attracted significant interest because of its promising photoelectric and photocatalytic properties, which are strongly governed by its electronic structure and carrier transport behavior. In this study, first‐principles density functional theory (DFT) calculations are performed to investigate the structural, electronic, carrier transport, optical, mechanical, and dynamical properties of cubic spinel ZnIn ₂ S ₄ . The optimized lattice parameter is calculated as 7.555 Å, showing excellent agreement with the reported value with only 0.605 % deviation. The electronic structure reveals an indirect semiconducting nature with bandgaps of 1.289 and 1.123 eV obtained from spin‐polarized and nonspin‐polarized GGA‐PBE calculations, respectively. The calculated electron and hole effective masses are 0.129 and 1.970 m _e , leading to estimated mobilities of 136.3 and 8.91 cm ² V ⁻¹ s ⁻¹ , respectively. Optical calculations demonstrate strong visible‐to‐ultraviolet light interaction with a static dielectric constant of 7.66, maximum refractive index of 3.34, and enhanced absorption response. Mechanical properties confirm structural robustness with a Hill bulk modulus of 75.896 GPa, Young’s modulus of 98.535 GPa, and Poisson’s ratio of 0.28362. Phonon dispersion analysis confirms dynamical stability through the absence of imaginary modes. These findings highlight cubic ZnIn ₂ S ₄ as a promising semiconductor for light‐responsive and optoelectronic applications.