Abstract: Chemisorption on a model bee metal*t

Chemisorption on a model bee metal*t W. Ho, S. L. Cunninghamt, and W. H. Weinberg Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125 (Received 4 September 1975; in final form 2 October 1975) PACS numbers: 82.65.M, 73.20. The system considered here is that of a single atom with one energy level chemisorbed on the (001) surface of a model bee metal. We present the change in the density of electronic states D.n (E) due to chemisorption for two cases: one when the adatom is bound to a single substrate atom in the "on-site" configuration and the other when it is bound to four substrate atoms in the "centered fourfold site." In principle, this change in the density of states D.n can be related to the results of photoemission measurements. 1 There are four reasons for this study: (I) By comparing with previous results of chemisorption on the (001) surface of a model simple-cubic metal, we can determine the sensitivity of D.n (E) to the substrate crystal structure. (2) We can investigate the sensitivity of D.n (E) to the binding site configuration. (3) The same model of the substrate can be easily extended to that of a two-band crystal with the CsCl structure. 3 Therefore the results of this work will serve as a basis for comparison with the results of a chemisorption study on a model insulator surface. (4) Finally, a simple modification of the present theory can be used to study the adsorption of a monolayer of atoms on the same surface. A comparison of D.n (E) calculated for a single chemisorbed atom with D.n (E) for a monolayer will be important for understanding experimental photoemission results. To model the bee metal substrate, we use the linear combination of atomic orbitals (LCAO) method and the tight binding approximation (TBA) to generate the electronic energy levels and wave functions. Each atom is assumed to have one orbital at energy E 1, and only nearest-neighbor overlap integrals y are considered. A complete description of the Green's functions appropriate for the (001) surface of this model metal has been presented elsewhere. 3 For the ada tom, we assume a single energy level of E a coupled to the surface with an interaction strength CJ'. The Green's function for this single level system is well known. 2 To obtain the change in the electronic density of states due to chemisorption, we follow the procedures used before• of determining the phase shift due to the perturbation potential associated with the formation of the chemisorption bond. This phase shift is the negative of the argument of the complex determinant of the matrix I-VG, where I is the unit matrix, V is the perturbation matrix, and G is a matrix containing the Green's functions for the adsorbed atom and the clean crystal surface. The change in the density of states D.n (E) is related simply to the derivative with respect to energy of this phase shift. 1.0