Massively parallel direct SCF calculations on large metal clusters: Ni5-Ni481

Summary The convergence of the cluster model with respect to excitation energies, ionization potentials and hydrogen chemisorption energy in the four-fold hollow site of the Ni(100) surface is studied for a sequence of cluster models from Ni₅ up to Ni₁₈₁. For the largest, Ni₄₈₁, cluster studied, only the structure of the occupied levels for one state is obtained. The concept of bond-preparation is found to be essential for the evaluation of chemisorption energies also for clusters with more than 100 atoms. The cluster excitation energies show a slow decrease such that even for Ni₁₈₁ the step between the lower excited states is still 0.1–0.2 eV. The effect ofp-functions on surrounding cluster atoms is found to be 3–4 kcal/mol independent of cluster-size. The direct SCF program DISCO was parallelized using the TCGMSG toolkit in order to perform the calculations. The easy strategy utilized is analysed and exhaustive timings on the Alliant Campus/800 MPP system with 200 CPU's are presented.