An extremely simple calculational method based on the effective medium theory is developed to describe chemisorption systems. It is tested for hydrogen chemisorbed on Ni(100) and (111). Good agreement with experiment is obtained for all quantities calculated: chemisorption energy, equilibrium position, vibrational frequency, and the energy of the hydrogen-induced level. The results indicate that hydrogen may exist under the first Ni layer of Ni(111), but that the binding here is weaker than outside the surface.

• Received 12 March 1982

DOI:https://doi.org/10.1103/PhysRevLett.48.1620