Chemisorption and repulsive physisorption potentials from a unified treatment

By using an extended Anderson's model Hamiltonian free from adjustable para meters, and where the atom-surface interaction system is built from the bas ic dimeric components, we show that the short-range contribution to the int eraction energy provides a unified basis for describing chemisorption and t he repulsive part of the physisorption potential. Using this, we analyse th e process of chemisorption of H on Al and Li surfaces by examining a variet y of crystalline faces and adsorption sites. The results are in good agreem ent with those obtained by different theoretical methods and also with the available experimental data. This model calculation is also applied to inve stigate the interaction of He with Al and Na surfaces. We calculate the rep ulsive contribution to the interaction energy covering five orders of magni tude on the energy scale. We find that it shows a Molliere-like dependence with increasing adsorbate-substrate separations. Also, we have verified tha t the differences in the physisorption potentials introduced by selecting d ifferent van der Waals attractive potentials may even be much larger than t hose caused by the differences in modelling of the repulsive potentials.