Adatom Adsorption Energy Dependence on Coordinative Unsaturation of Surface Atoms

Adatom Adsorption Energy Dependence on Coordinative Unsaturation of Surface Atoms 

we analyze the electronic details of the surface chemical bond based on state-of-the-art DFT electronic structure calculations [5]. We address the relation between bond energy of the adatom as a function of its coordination number with the surface atoms as well as coordinative unsaturation of the surface atom, defined by its coordination number with neighbor metal atom N. We illustrate this in a detailed discussion of the chemisorption of a C atom to dilferent surfaces of Ru. In the DFT calculations, the surface is modeled as a metal slab chosen with enough metal layers that energies become independent of layer thickness. The surface atom positions and distances change slightly in contact with the adsorbate, because of the weakened metal atom-metal atom bond by interaction with the adsorbing atom. 

It is important to distinguish first-sheU coordination of the adsorbate and second-shell coordination number of surface atoms with surrounding metal atoms, as is shown in Table 10.1. 

In Table 10.1 [3], a comparison is made of computed adsorption energies of C atoms attached at difierent sites on dilferent surfaces of Ru. The energies have been ranked according to the coordination number of the C atom, which is the first number in the fourth column of Table 10.1. The number within brackets in 

A clear trend is observed as long as the coordination number of the C atom does not change, its interaction energy will increase when the coordinative unsaturation of the metal surface atom increases. This trend predicted in the previous section is confirmed by the more rigorous quantum-chemical DFT results of Table 10.1. The adsorption energy of the C atom increases with increasing surface metal atom coordination number N. This relates to the C atom valency, as is discussed in detail in Section 10.3.5. 

---