Density functional theory study of CO adsorption on the (1 0 0), (0 0 1) and (0 1 0) surfaces of Fe₃C

Density functional theory (DFT) calculations have been carried out on the adsorption of CO on the (1 0 0), (0 0 1) and (0 1 0) surfaces of Fe₃C. Both (1 0 0) and (0 0 1) have surface iron and carbon atoms, while (0 1 0) has only surface iron atoms. At 1/5 ML on (1 0 0), the most stable adsorption configuration has adsorbed CO at a three-fold site (three Fe atoms), followed by adsorbed surface ketenylidene at a four-fold site (three iron atoms and one carbon atom). At 1/6 ML on (0 0 1), the most stable adsorption configuration has adsorbed CO at a four-fold site (four iron atoms). With increased coverage, adsorption at different sites becomes possible and close in energy. On the metallic (0 1 0) surface, both two-fold and three-fold adsorptions are close in energy. The electronic states of the most stable adsorption structures have been analyzed accordingly.