Adsorption studies of isoxazole derivatives as corrosion inhibitors for mild steel in 1M HCl solution: DFT studies and molecular dynamics simulation

Abstract A series of organic compounds derived from isoxazole, namely 4a, 4b, 4c, 4d, 4e, 4f, 4g and 4h were studied as corrosion inhibitors for mild steel in order to investigate the influence of different substitutions on the overall intrinsic properties such as boundary orbital energies (EHOMO, ELUMO), energy gap ∆E, electronegativity χ, absolute hardness η, and softness σ, fraction of transferred electrons ∆N; and local such as natural atomic populations and Fukui indices. For this purpose, theoretical studies have been carried out by the DFT density functional theory at the level of the B3LYP functional and the 6-31G (d,p) basis set. As well as, the simulation study of the molecular dynamics was carried out on the surface of Fe (110) in order to understand in depth, the adsorption behavior of the studied inhibitors. Indeed, in this context, the impact of the different groups in the inhibitors before and after adsorption on the iron surface. The optimized structures, electronic parameters, FMOs, Fukui functions and thermodynamic parameters were evaluated to identify candidates appropriate for application as corrosion inhibitors. The results of the global descriptors of the eight isoxazole derivatives showed that these descriptors are almost similar except for compound 4c, these studied inhibitors act in a similar manner. Moreover, the molecular dynamics results also discovered that these inhibitors represent a better reactivity as a result of the negative value of the adsorption energy of all the studied compounds which shows that, these adsorbed systems are more stable and stronger. The results of the dynamic descriptors found by MDS were in excellent coherence with the quantum study results.