MODEL STUDY IN CHEMISORPTION - MOLECULAR-ORBITAL CLUSTER THEORY FOR ATOMIC-HYDROGEN ON BE(0001)

The interaction between atomic hydrogen and the (0001) surface of Be has been studied by using clusters of Be atoms to simulate the substrate. The largest cluster used contains 22 Be atoms, 14 in the first layer and 8 in a second layer. An H atom is added to the Be clusters at four high symmetry adsorption sites. Ab initio molecular orbital Hartree-Fock wave functions have been obtained and the interaction energy of H with the Be cluster is studied as a function of vertical distance from the surface. Thorough studies of various aspects of the computations and of the appropriate interpretation of the cluster results are reported. The authors' results show that three of the sites considerd have similar binding energies, D//e approximately equals 50 kcal/mol ( approximately equals 2. 1 multiplied by 10**5J/mol), and (vertical) equilibrium distances from the surface, r//e approximately equals 0. 1 nm. For the fourth site, H directly over a Be atom, D//e is approximately equals 30 kcal/mol (1. 3 multiplied by 10**5J/mol), and r//e is approximately equals 0. 14 nm.