Chemisorption effective medium theory

A simple picture of chemisorption comes from effective medium theory (Nprskov and Lang, 1980), based on the idea (related to density-functional theory, sect. 2.1) that to a first approximation the adsorption energy at point... 

Figure 6.1. Chemisorption energies of hydrogen and oxygen on transition metals across the periodic table that were calculated using the effective-medium theory and also measured on polycrystalline surfaces (231.

Effective medium theory was originally introduced in the early 1980s to describe chemisorption of gas atoms on metal surfaces. It has since been developed as a relatively efficient method for describing bonding in solids, particularly metals, and therefore has found considerable use in materials model-ing. It also forms the quantum mechanical basis for the more empirical and widely used embedded-atom method discussed below. Specific implementations of effective medium theory for materials simulation have been developed by Norskov, Jacobsen, and co-workers and by DePristo and co-workers. ... 

The work-function dependence according to Eq. (28) results in similar effects of the electrostatic field on chemisorption as found from first-principle calculations [11], effective medium theory [10], or adapted extended Hiickel theory [55]. 

Chemisorption of H on simple metals and on transition metals has been studied theoretically using approaches such as molecular orbit theory, valence bond theory, density functional theory, cluster calculations (a detailed description up to 1980 can he found in Smith, 1980), and effective medium theory (N rskov, 1984). An extension of the effective medium theory, the so-called embedding atom method - originally developed to study the embrittlement problem - was shown to yield very valuable results for H on metals, particularly for the surface relaxation and the H adsorption sites including subsurface sites (see Pd) (Daw and Baskes, 1984). 

Numerous theoretical approaches have been employed to investigate the details of oxygen chemisorption including the semiempirical effective medium theory (EMT) [3], the tight binding theory [4—6], the first-principle method [7, 8], and the density function theory (DPT) [9-14]. 

In the effective medium theory, the electronic interaction between an atom and the solid is replaced by that of the atom and a homogeneous electron gas. The approach is based upon density functional theory, but since the solid is not really behaving as a homogeneous electron gas, gradient corrections to the theory have been devised [210]. Simple model hamiltonians have also been used to study chemisorption of atoms and molecules at metals. Here we mention the Anderson-Grimley-Newns model hamiltonian of the type... 

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