Metal surfaces, electronic structure density approximation

In order to comprehensively show the chemical dissociation process of CO on metal surfaces, electronic structure calculations have been performed for simple models. We have chosen two methods for the present analyses. The first method is the Discrete Variational Xa (DV-Xa) method, which is the first-principles molecular orbital calculation using Slater s Xa fimctional for the electron many body term [21]. This method is applied for the electronic structural analyses of CO adsorption on metal surfaces. The second method is the Full-Potential Linear Muffin-Tin Orbital (FP-LMTO) method, which is the first-principles band structure calculation method [22]. The FP-LMTO implementation code of LmtART [23, 24] is used for the calculations of the density of states (DOS) of non-magnetic fee iron phase. We discuss the electronic structure of transition metal alloys from the rigid band analyses using this DOS. The local density approximation (LDA) parameterized by Vosko et al. [25] is used for the present FP-LMTO calculations. The tetrahedron... 

In the next chapter results of accurate quantum-chemical calculations on transition metal surfaces will be presented. Here we will develop a method that enables an estimate of elementary quantum-chemical features, without the need for extensive quantum-chemical calculations. The result is of limited and only qualitative value and we will verify it in the next chapter with the aid of more sophisticated procedures. The method is of use to us because it permits the development and illustration of concepts that will facilitate our analysis of more advanced calculations. In this section we will analyze the electronic structure of a face-centered cubic (f.cx.) transition metal. We will use the method to discuss the valence electron structure of the (lll)i (100) and (110) surfaces of f.c.c. crystals. Specifically we are interested to know whether subbands can be identified, whose bandwidths can be estimated by means of the Bethe lattice approximation and how their respective local densities of states behave as a function of valence electron band filling. 

The fact that electrons tend to spill out from the metal reflects the mobility of the electron gas within these systems. The distance involved in the formation of the surface dipole is approximately 100 pm. The exact value of x depends on the crystallographic structure of the metal at the surface and reflects the density of metal atoms associated with this structure. For metals with a low melting point, the data for the polycrystalline surface recorded in table 8.2 give the best indication of surface properties. Since the metal atoms are relatively mobile at room temperature, the system tends to maintain the properties described in the jellium model at the surface. 

---