3) developing bulk iron-oxides. The measured results from corrosion studies warrant further study at the atomic and molecular level. DFT calculations are employed to understand the oxygen structures and orientation on the iron surfaces. Figure (a) and (b) above give the setup of the adsorption sites on Fe(110) and Fe(100), respectively. DFT studies on the Fe(100) and Fe(110) surfaces indicated that the fourfold hollow sites of Fe(100) and long bridge sites of the Fe(110) surface are the most stable adsorption sites for atomic oxygens up to monolayer coverage. However, other studies suggested that threefold hollow sites of Fe(110) are more stable for oxygen adsorption. Bader charge transfer analysis of oxygen atom adsorbed iron surface showed significant charge transfer towards the oxygen atom as illustrated in Figure (a). Figure (b) shows the average positions of adlayer oxygen atoms and surface iron atoms as a function of the coverage. The average position of the oxygen atoms almost stayed constant for Fe(100) while it gradually increased for Fe(110). The atomic adsorption at low coverages was found to be strong and while the coverages increased, the adsorption became weaker due to the steric repulsions (Figure (c)). Nevertheless, decrease in adsorption energy with surface coverage is less pronounced on the Fe(100) than on the Fe(110) surfaces. Such continuing decrease in the Fe(110) surface is due to the highly dense packed nature of the iron atoms which resulted in strong lateral steric repulsion for adsorbed oxygen atoms. For instance, adsorption energy at 0.25 ML is highest for Fe(110) and decrease significantly at 1 ML. On the Fe(100) surface, the adsorption energy gradually reduced with the increase of the oxygen coverage.