The convergence of the cluster model for the study of chemisorption: Be₃₆H

Abstract

A three layer cluster (with 14, 8, and 14 atoms comprising the three layers) has been used to model the chemisorption of atomic hydrogen on the (0001) surface of beryllium. Ab initio molecular electronic structure theory was employed at the self-consistent field level with a minimum basis set (Be, 1s, 2s, 2p, and H 1s functions). The properties of the Be36 cluster are discussed in some detail, as is the adsorption of H on each of four different high-symmetry surface sites. Significant differences are reported for chemisorption on this model surface relative to the results obtained previously with a two-layer Be22 cluster. Changes in chemisorptive bond energies range from 0.2 to 9.7 kcal, while BenH distances change by 0.01 to 0.04 Å in going from Be22 to Be36. It is concluded that some properties related to chemisorption converge reasonably rapid with respect to cluster size, e.g., bond distances, while others, e.g., dissociation energies, converge more slowly. © 1983 American Institute of Physics.