Physical approaches to the metal-oxide interface

Atomistic simulations of the metal-oxide interface can be basically classified under two main groups depending on the representation of the substrate. The first approach is constituted by the cluster model, where a piece of material is made to represent the whole substrate. The second approach is the periodic approach where a selected part of the material is repeated in space thus taking advantage of the periodicity of the crystal (Fig. 2.1). 

An introduction of the surrounding effects for very ionic materials, like MgO, is in principle, relatively easy. The main term here is the inclusion of 

The cluster model approach can be viewed as the chemist s approach since it reduces a very large system to a supermolecule, yet it is currently the only way to study excited states and therefore to contribute to the interpretation of electronic spectra. On the other extreme, one finds the physicist point of view, which makes uses of translational symmetry and treats the system as a perfect periodic solid. Therefore, as in the cluster model approach, the periodic approach constitutes a severe approximation since the same structure is reproduced in two or three space directions. 

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