Corrosion inhibition mechanism of Eupatorium capillifolium extract on mild steel: Insight from experimental and molecular dynamics simulations

This study investigates the corrosion inhibition performance and mechanism of Eupatorium Capillifolium extract on mild steel in 0.5 M H 2 SO 4 media through a combined experimental–computational approach. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP) revealed a maximum inhibition efficiency of 91.1% at 2.0 gL -1 with a cathodic inhibition mechanism. Surface morphology from SEM indicated smooth, passivated layers in inhibited samples. Density Functional Theory (DFT) and Molecular Dynamics (MD) simulations identified Methyleugenol (MEG) as the principal active phytoconstituent exhibiting the most favorable adsorption energy (−98.48 kcal mol −1 ) on Fe (110). Protonated MEG (MEGH + ) displayed the smallest HOMO–LUMO gap (3.16 eV), highest dipole moment (8.98 D), and strongest Fe–inhibitor interaction, corroborating experimental efficiency. Radial distribution function (RDF) analysis further confirms the formation of a stable adsorbed layer dominated by chemisorption interactions. The combined experimental and theoretical results demonstrate that the inhibition mechanism involves synergistic physisorption–chemisorption processes mediated by π-electron interactions and lone-pair electron donation to the metal surface. These findings highlight Eupatorium capillifolium extract as a promising, environmentally friendly corrosion inhibitor for mild steel in acidic environments and demonstrate the effectiveness of combining electrochemical techniques with multiscale molecular simulations to elucidate corrosion inhibition mechanisms.