Approach to the embedding problem in chemisorption in a self-consistent-field-molecular-orbital formalism

A solution for the embedding problem in chemisorption is proposed, particularly designed for easy implementation into molecular-orbital linear-combination-of-atomic-orbitals self-consistent-field calculation schemes. It is essentially based on the assumption that the perturbation in the electronic states induced by the adspecies is effectively screened within a certain $B$ region of the adsorbing solid and that this $B$ region is also large enough to allow for neglect of direct-coupling terms between the adspecies and the defective solid. An energy-dependent coupling matrix $M\left(e\right)\mathrm{}$ is defined, which may be calculated on the basis of the free-solid solution and that can be used to correct the local solutions so as to properly connect them to the free-solid ones. The theory is tested in the case of hydrogen adsorption on graphite in the complete neglect of differential overlap approximation. Moderately large embedded clusters appear to be adequate for a correct description of the chemisorption process.