Theoretical Descriptions of the Metal Surface

The chemist s mind may have some difficulty in grasping the concept of a band structure and LDOS for a single atom (e.g. at a kink site), but it may be helpful to remember that band width is a variable feast, increasing with the number of adjacent atoms of like type. There can therefore be all widths from the full width 

The original work and these further developments relate only to the fee structure, which accounts for the most catalytically interesting and useful metals, but the concept can be extended to the bcc and eph structures using the orbital assignments given many years ago by Trost and others. In these cases however it is essential to use hybrid orbitals having d, s and p components. 

Returning for a moment to the description of bonding inside the crystal, those d-orbitals whose interactions are responsible for bonding nearest neighbours (viz. the t2g family) will form a band which is broader than that formed by the 6g family, since interactions between next-nearest neighbours are less strong. Extending this concept to surface atoms, we see on the (KX)) surface for example that the absence of atoms above the plane means that the overlap of dxz and d y orbitals has decreased and their band is narrowed, while the dyz orbitals in the surface plane are unaffected, and their band remains broader. Similar but smaller effects will occur with the Cg and 5-orbitals. The modification of electronic structure of atoms at steps and kinks is then easily rationalised, and the story will be resumed in Chapter 2, where other concepts developed in the context of small metal particles will be considered. 

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