The 3rd Cl− prefers to occupy the O(5) site with the Eads of -0.903 eV, which is lower than the Eads of O(2)O(8) configuration with -0.847 eV. When Cl− adsorb at O(5) atop site, the data of dCl-Al(1) with 2.529 Å are smaller than O(2)O(8) configuration with dCl-Al(1) of 2.919 Å, these lead to the largest data of dAl(1)-O(2) with 0.685 Å than all the other adsorption configurations above. But the Eads, Ebslab and EbCl of O(5) configuration are close to the data of O(2)O(8) configuration. On one hand, the more Cl− adsorb, the more surface Al atoms be pulled out substrate; on the other hand, no BU 226 Cl− occupying or not in one ML plane, the Al2O3 substrate are still not obvious breakdown by these Cl−. The reason maybe up-layer Cl− interact with down-layer (adlayer) Cl− strongly and directly, this leads to the dispersion of interactions between adlayer Cl− and surface substrate atoms, the absolute value of Eads between chloride ions and surface Al atom always much smaller than the absolute value of Ebslab between Al atoms of substrate, so the reaction product on the surface cannot generate without enough electrons and energies transferred from Cl−. In another word, instead of dissociating the oxide film, more than three Cl− together adsorption would restrain surface corrosion to happen. Altogether, the breakdown of passive film would needed more kinds of local interaction of polarity ions.