LOCAL AND NONLOCAL DENSITY FUNCTIONAL-STUDY OF NI4 AND NI5 CLUSTERS - MODELS FOR THE CHEMISORPTION OF HYDROGEN ON (111) AND (100) NICKEL SURFACES

The results of density functional calculations using the local density approximation and the self-consistent implementation of density gradient type nonlocal corrections to exchange and correlation are reported for the nickel dimer and for Ni4 and Ni5 clusters. Using these clusters as models for (111) and (100) Ni surfaces the chemisorption energies for atomic hydrogen are also presented. The idea of Siegbahn to prepare the cluster for chemisorption by making a proper excitation to a bonding state has been examined. Using this approach, the chemisorption energy from calculations on these very small nickel clusters agrees very well with the experimental surface data, when nonlocal corrections are included. Chemisorption energies as well as electronic properties of the bare nickel clusters are discussed in the context of local and nonlocal treatments of exchange and correlation.