Green function adatom

Turning to the chemisorption situation portrayed in Fig. 3.2, we require the potential-bond operator 

Alternately, by introducing the so-called reduced self-energy 

Let us now explore the DOS situation outside the band (i.e., X 1), where the reduced energy Xtt of the localized adstate is given by the zeros of the denominator of the GF (3.25), which is written as 

Equations (3.38) and (3.48) are the analytical expressions for the band and adstate contributions to the total reduced-energy spectrum of the adatom DOS, pa(x), respectively. Their graphs are displayed in Fig. 3.4 for 2/3 = 1 and the parameter values indicated. As can be seen, the presence of the large adstate spike at X = Xa markedly reduces the area under the in-band portion of the DOS, in accordance with the sum rule (cf. (3.34)) 

We note that the p()(X)-curve attains its maximum value at X = Xy1, being given by 

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Stepanyuk et al. [471] have applied local approximation of the density-functional theory and the Korringa-Kohn-Rostoker (KKR) Green s function method to determine the energy of Co adatoms located at the ideal Au(lOO) surface. Total-energy calculations have shown that Co atoms and small Co clusters are preferably embedded inside the substrate. 

In the late 1980s, Feibelman developed his Green s function scattering method using LDA with pseudopotentials to describe adsorption on two-dimensionally infinite metal slabs [175]. based on earlier work by Williams et al [176]. The physical basis for the technique is that the adsorbate may be considered a defect off which the Bloch waves of the perfect substrate scatter. The interaction region is short-range because of screening by the electron gas of the metal. Feibelman has used this technique to study, for example, the chemisorption of an H2 molecule on Rh(OOl) [177]. S adatoms on Al(331) [178] and Ag adatoms on Pt(l 11)... 

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