Quantum and dynamic investigations of Complex iron- alkaloid-extract Cytisine derivatives of Retama monosperma (L.) Boiss. Seeds as eco-friendly inhibitors for Mild steel corrosion in 1M HCl

Abstract In this study, the adsorption of Cytisine derivatives as an eco-friendly inhibitor for mild steel corrosion [ 1 , 2 ] on the iron surface was modeled using density functional theory (DFT) calculations and the Monte Carlo (MC) as well as Molecular dynamics (MD) simulations to elucidate the interactions involved. Firstly, the interaction of these inhibitors with iron clusters Fen (n=1-5) was studied by DFT as a representative example of a corrosion inhibition process. Moreover, structures, binding energies, partial atomic charge NBO and natural bond orbital analysis of the resulting complexes support the existence of considerable binding between these inhibitors and Fen (n=1-5) clusters. Then, the dynamic Monte Carlo (MC) simulation was also adopted to simulate the adsorption of Cytisine derivatives on the iron Fe (111) surface in vacuum as well as in acidic solution containing 491 H2O, 4 hydronium ion H3O+ and 5 chlorine ion Cl−. Besides, to advance the understanding of interactions between these molecules and iron surface, the radial distribution function (RDF), mean square displacement (MSD) and fractional free volume (FFV) were also studied in this paper. Our results of both the Fen (n=1-4) clusters and the Fe (111) surface made it possible to show noticeable competitiveness between the three protonated inhibitors with a slight superiority for the n-CytN9H+ molecule. Furthermore, based on the diffusion coefficient we found that the three protonated inhibitors have a good capacity to slow down the movement of corrosive particles and consequently to inhibit the metallic substrate against corrosive electrolyte.