STRUCTURE AND BONDING IN SMALL ALUMINUM CLUSTERS

Density-functional calculations with simulated annealing have been performed for aluminum clusters Al(n) up to n = 10. There are many local minima in the energy surfaces, with a rich variety of structures and spin multiplicities. With increasing cluster size we find transitions from planar to nonplanar structures at n = 5, and to states with minimum spin degeneracy at n = 6. There are stable isomers of Al5-Al10 with buckled planar structures reminiscent of the layers in crystalline alpha-gallium. All structures show regular patterns of bond and dihedral angles. Trends in binding and ionization energies are compared with experiment and with the predictions of other calculations.