A theoretical approach to the corrosion inhibition of iron in acidic solution by a green formulation derived from Nigella sativa L seeds oil

A theoretical approach combining density functional theory (DFT) computation, Monte Carlo (MC) methods, and molecular dynamics (MD) simulations was used to investigate and validate the iron corrosion inhibition performances in the acidic medium of a green formulation based on the oil extracted from Nigella sativa L. DFT calculations allowed to determine the energetic, global, and local chemical reactivity parameters. The most stable adsorption configuration of the fatty acids components of the Nigella sativa L. formulation was determined by the Monte Carlo methods with the adsorption locator module and by molecular dynamics simulations. Results indicated that all the compounds are absorbed with a totally flat orientation on the first layer of the metal surface. The active sites of molecules were effectively established by using DFT through the analysis of frontier molecular orbitals (FMO), the Hirshfeld population analysis (HPA), the electrostatic potential (ESP), molecular electron density analysis (MED), and Fukui indices (FI). The solvent effect was investigated by using the conductor-like polarizable continuum model (CPCM). Protonation effects were also analysed through the protonation energy (PE), the proton affinity (PA), and the absolute gas phase basicity (GB). The formation of a coating on the iron surface validated the good protective action of the green formulation derived from Nigella sativa L. The computational and theoretical approaches substantiate our experimental electrochemical and spectroscopic studies [1].