ATOMIC-HYDROGEN INTERACTION WITH METALLIC LITHIUM - AN AB-INITIO EMBEDDED-CLUSTER STUDY

The interaction of atomic hydrogen with metallic body-centered-cubic lithium is theoretically investigated by means of an ab initio Hartree-Fock embedded-cluster technique. Both hydrogen adsorption on thin films parallel to the (001) face, and its diffusion in bulk lithium as an interstitial impurity are considered. In the former case, supercell calculations are also performed concerning periodic hydrogen overlayers. The results show that hydrogen is adsorbed with appreciable energy (6080 kcal/mol) on lithium (001), and can migrate almost freely in the surface layer; its penetration deeper into the lattice seems to require overcoming a modest but not negligible activation barrier (1015 kcal/mol). The adsorption-energy data obtained here are somewhat larger than those resulting from isolated cluster studies. In all configurations H attracts electrons from the metal. This negative local charge is effectively screened within a small number of shells of neighbors; in some instances, depletion of electrons takes place more effectively from second than from first neighbors of H. For high-surface concentrations of adsorbed H, an ionic overlayer is formed, the ionicity decreasing with concentration, in accordance with previous results. © 1995 The American Physical Society.