Table : Comparison of adsorption energies and average Cl-Fe bond lengths obtained with and without vdw correction. Chloride ion's ability to depassivation was analysed using DFT calculations on a simple Fe(100) surface model. In their study, Ming et al. revealed that the co-adsorption of Cl⁻ on the Fe(100) surface can weaken the Fe-O bond and reduce the charge transfer from the Fe surface to O atoms, thereby facilitating depassivation. Similarly, detailed dynamic interactions of the Fe/Cl system were studied using reaxFF-MD simulations. The parameters for the Fe/Cl system were generated by DFT calculations using FeCl3, Fe2Cl6, Fe(OH)2Cl, Fe(OH)Cl2 configurations. The simulation system of Fe(100) surface and 1 mol/L chloride solution was used, and simulation was carried out for 500 ps as shown in Figure (a). The total system included Fe atoms, H2O molecules, and Cl⁻, Na + , and OH⁻ ions. At the initial stage of the simulation, it has shown the accumulation of chloride ions at the iron surface. Such Cl-Fe interaction leads to the distortion of iron surface lattice and results in the dissolution of iron atoms partly into the solution as iron chloride compounds as shown in the 11.7 ps snapshot of Figure (b). On the contrary, some of the undissolved iron atoms react with hydroxyl groups to form iron hydroxide compounds at the interface as seen in Figure (b). This lattice alteration ability of Cl⁻ ions is attributed to its catalytic effect, and this officially marks the initiation of (c). The former represents the iron-oxide bond in the surface oxide layer whilst the latter is corresponding to the coordination between the oxygen of water and dissolved iron atoms. The RDF of Fe-Cl resulted in a peak at 2.35 Å, aligning closely with the experimental value of the bulk Fe-Cl bond (2.32 Å). Considerable charge transfer can be seen at the interface as shown in Figure (e). The most obvious changes are from iron and oxygen atoms, where iron atoms transition to higher valence state by losing electrons while oxygen atoms gain the electrons to become more negatively charged at the oxide layer. This charge transfer phenomenon progresses the corrosion process. Moreover, an increase in the external electric field and temperature led to an increase in the corrosion rate. Overall, this study provided valuable insight into atomic scale chloride-induced corrosion behaviour at the iron surface. Reprinted with permission from Elsevier. Chloride-induced depassivation mechanisms have been proposed through extensive mechanistic studies. Among these, the ion exchange model and the point defect model are the most popular. Both mechanisms begin with the adsorption of Cl⁻ ions on the passive layer. The point defect model suggests that Cl⁻ ions occupying oxygen vacancies catalyse the formation of iron vacancies in the passive film. These iron vacancies travel through the passive film towards the metal/metal oxide interface, while oxygen vacancies travel in the opposite direction. Finally, iron vacancies at the metal/metal oxide interface combine to make voids, leading to the deterioration of the passive layer in Figure M. The initial and final configurations of the simulations are shown in Figure Reprinted with permission from Elsevier. Thermodynamic feasibility of the above-mentioned four-stage mechanism for chlorideinduced depassivation was studied using DFT calculations. indicated the tendency for Cl⁻ ions to be replaced by OH⁻ ions. However, when the hydroxyl concentration was reduced, surface Fe-Cl compounds were generated, and due to their lower stability, they easily detached from the surface. This was further supported by vacancy formation energy calculations, which showed that forming vacancies by removing Fe-Cl compounds required less energy than removing Fe-OH compounds. In a seminal study, Du et al. investigated the impact of chloride ions on carbon steel using a model with 0.1% carbon uniformly distributed into the iron matrix. They observed that at elevated temperatures (400 K), low-coordinated Fe-C compounds (Fe2C and Fe3C) could form within the passive film due to the dynamic formation of the film. These compounds can interact with water to form CO gas, exhibiting the decarburization phenomenon of carbon steel.