<p>The single-In-atom-doped Cu-based clusters exhibits high catalytic activity in CO₂RR, which is selective to CO with a maximum faradic efficiency, such as the InCu₉₉ cluster [Angew. Chem. Int. Ed., 2025, 64(43): e202512970]. However, the structure evolutions and electronic properties of In doped Cu clusters have not yet been fully clarified. Here, the growth patterns and superatomic properties of InCu_n (<i>n</i> = 1–9) clusters are first analyzed using the genetic algorithm combined with the density functional theory (DFT). The structural transitions of them are found to occur at the InCu₄, where the In atom trends to stabilize at the vertex sites with high-coordination numbers. Among them, the octahedral InCu₅ has a higher stability than that of its neighbors on the average binding energy per atom (<i>E</i>_b), the fragmentation energy (<i>E</i>_f) and the second-order differences of energy (Δ₂<i>E</i>) curves, and can maintain the structural integrity at 700&#xa0;K. The molecular orbitals reveal that the InCu₅ has a 1<i>S</i>²1<i>P</i>⁶&#xa0;superatomic electronic shell, which is further confirmed by the electron localisation function (ELF), localised orbital locator (LOL) and density of states (DOS) analysis. The electrostatic potential surfaces confirm the presence of significant σ-hole regions at the Cu atomic sites. These σ-holes induce a red-shift in the C-O stretching frequency and an associated bond elongation, which originates from the donation of Cu 3<i>d</i>¹⁰ electrons into the anti-bonding π* orbital of CO.</p>