Theoretical studies of nickel clusters and chemisorption of hydrogen

First principles calculations of high- and low-symmetry clusters (up to Ni87) are reported. Macroscopic properties [ionization potential (IP), electron affinity (EA), and bandwidth] are not sensitive to cluster symmetry and, except for EA, are converged to bulk values by Ni87. Even for Ni87 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 ∠3 eV for both types of sites. Geometries are not cluster sensitive with R (NiH) values of 1.57, 1.62, and 1.78 Å for twofold, threefold, and fourfold sites, respectively. Vibrational frequencies for these sites are 1420, 1212, and 592 cm−1, respectively.