The adsorption of CO molecules on a Pt 111 surface can be significantly affected by the presence of surface defects. Density functional theory DFT calculations have been used to predict and understand these effects. Some of the key findings are:1. Adsorption energy: Surface defects can alter the adsorption energy of CO molecules on the Pt 111 surface. In general, CO molecules tend to adsorb more strongly at defect sites compared to the perfect Pt 111 surface. This is because the defects create new adsorption sites with different electronic and geometric properties, which can lead to stronger interactions between the CO molecules and the surface.2. Adsorption sites: Surface defects can create new adsorption sites for CO molecules, such as step edges, kinks, and adatoms. DFT calculations show that these sites can have different adsorption properties compared to the regular Pt 111 surface. For example, CO molecules may adsorb in a more tilted orientation at step edges, which can affect their reactivity.3. Surface reconstruction: The presence of CO molecules can induce surface reconstruction, especially at defect sites. DFT calculations have shown that the adsorption of CO can cause the surface atoms to rearrange, leading to changes in the local geometry and electronic structure. This can further affect the adsorption properties of CO molecules on the Pt 111 surface.4. Reactivity: Surface defects can influence the reactivity of adsorbed CO molecules. DFT calculations have shown that CO molecules adsorbed at defect sites can have different reactivity compared to those adsorbed on the perfect Pt 111 surface. This can be important for catalytic reactions involving CO, such as the water-gas shift reaction or the oxidation of CO to CO2.5. Coverage dependence: The effects of surface defects on CO adsorption can be coverage-dependent. At low CO coverages, the defects may have a more pronounced effect on the adsorption properties, while at high coverages, the CO molecules may interact more with each other, reducing the influence of the defects.In summary, surface defects can significantly affect the adsorption of CO molecules on a Pt 111 surface, as predicted by density functional theory calculations. These effects can influence the adsorption energy, adsorption sites, surface reconstruction, reactivity, and coverage dependence of CO adsorption, which can be important for understanding and optimizing catalytic processes involving CO molecules.