This work presents a first-principles study of the structural and electronic properties of the (InSb)1-x(Sn2)x solid solution using density functional theory within the Quantum ESPRESSO framework. The results show that Sn incorporation modifies the electronic structure while preserving the direct band-gap nature of InSb, with the valence-band maximum and conduction-band minimum remaining near the Γ point at low concentrations
(x = 0.05). The presence of Sn introduces additional states and perturbs the band dispersion near the Fermi level. A modification of the band gap is
observed, consistent with alloying effects in narrow-gap semiconductors. Despite the known underestimation of the band gap by semilocal approximations, the results provide a reliable qualitative description. Overall, even a small amount of Sn significantly influences the electronic
properties of InSb, indicating its potential for band-gap engineering and optoelectronic applications.