Structure-dependent adsorption of terpineol isomers on α-Fe(110): Atomistic insights from SCC-DFTB calculations

The adsorption of terpineol isomers on iron surfaces has attracted growing attention because of their potential as green corrosion inhibitors. In this work, theoretical calculations are performed to investigate the adsorption behavior of α-terpineol, β-terpineol, γ-terpineol, δ-terpineol, and terpinen-4-ol on the α-Fe(110) surface. We analyze adsorption geometries, adsorption energies, charge transfer, charge density differences, and electronic structures to establish the relationship between molecular structure and adsorp-tion performance. The calculated adsorption energies reveal a marked dependence on the molecular configuration, following the order α-terpineol > γ-terpineol > δ-terpineol > terpinen-4-ol ≈ β-terpineol. The strongest adsorption is associated with nearly par-allel molecular orientations that maximize interactions among the hydroxyl oxygen, the C C bond, and adsorbent atoms. Charge density difference and projected density of states show significant charge redistribution and pronounced hybridization between O 2 p /C 2 p orbitals and Fe 3 d states, indicating that adsorption arises from both chemical bonding and dispersion interactions involving the hydrocarbon scaffolding. Structural analysis reveals that shorter Fe O distances and favorable C–O–Fe angles correlate with enhanced adsorption stability. Among the configurations analyzed, α-terpineol shows the strongest adsorption on α-Fe(110) in the isolated-molecule limit. These results support the development of sustainable, bio-based green corrosion inhibitors for steel protection.