THEORETICAL STUDIES OF NICKEL CLUSTERS AND CHEMISORPTION OF HYDROGEN.

First principles calculations of high- and low-symmetry clusters (up to Ni//8//7) are reported. Macroscopic properties left bracket ionization potential (IP), electron affinity (EA), and bandwidth right bracket are not sensitive to cluster symmetry and, except for EA, are converged to bulk values by Ni//8//7. Even for Ni//8//7 the EA is over 2. 5 eV smaller than the IP; the origin of this effect is discussed. The chemisorption of hydrogen is considered on the low-symmetry clusters, where it is found that threefold and fourfold sites are most favored with bond energies of similar 3 eV for both types of sites. Geometries are not cluster sensitive with R (NiH) values of 1. 57, 1. 62, and 1. 78 A for twofold, threefold, and fourfold sites, respectively. Vibrational frequencies for these sites are 1420, 1212, and 592 cm** minus **1, respectively.