Theoretical study of the site dependence of the surface vibrational frequencies of H adsorbed on a Be surface

The interaction of H with the (0001) surface of Be has been studied using clusters of Be atoms chosen to simulate the substrate. The H atom has been placed at four different adsorption sites. Ab initio Hartree-Fock calculations are performed to obtain the interaction energies at various vertical distances of H from the surface. Vibrational energies are obtained from these Hartree-Fock results. The vibrational energies are substantially different for different surface coordinations of the adsorption sites. Force constants have been obtained from a simple model which connects the H with springs to the nearest substrate atoms. However, the spring constants for different sites are not equal but rather the sums of the force constants are equal. (Auth.)