Theoretical evaluation of spirocyclic compounds as green corrosion inhibitors for carbon steel

The Corrosion inhibition efficiency of some spirocyclic compounds in the presence of HCl 0.1 M as a corrosive electrolyte was explored using density functional theory (DFT) calculations and molecular dynamics (MD) simulations. All DFT calculations were performed using B3LYP functional in conjunction with 6-31+G(d) and 6-311++G(d,p) basis sets at both gas and solvent phases for protonated and neutral forms of inhibitory molecules. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels, HOMO-LUMO energy gap, quantum molecular descriptors, and thermochemical parameters were calcu-lated to determine the most effective corrosion inhibitors. MD simulations revealed that the adsorption energies (Eads) of the inhibitors on steel are dependent on the number of molecules introduced in the simulated systems. The more inhibitory molecules are adsorbed on the Fe substrate, the more anti-corrosion effect they have. The most negative Eads value observed occurs at 308 K, while it decreases at 318 K for all the other simulated systems, resulting in one of the molecules being identified as a potential carbon steel corrosion inhibitor for further experiments.