HUCKEL MODEL FOR METAL-CLUSTERS - GROUND-STATES AND LOW-ENERGY ISOMERS

Huckel model with ones-electron per atom is used to study the geometri es and electronic structures of clusters of 9 to 22 atoms. Two differe nt optimization schemes for obtaining the ground states are used; (i) minimization of an approximate Huckel ground state energy starting fro m a random geometry and (ii) simulated annealing. Both methods give si milar and new ground state geometries for clusters with 10 to 14 atoms . All clusters with more than 10 atoms will be distorted if the bond d istance is allowed to vary +/-5.5%. The ground states of clusters with atoms 10, 11, 12, and 14 are found to have the N=9 cluster as the bas ic building block, whereas the N=13 cluster is a distorted cuboctahedr on. As a general trend, the deformation of clusters increases from ato m number 8 to 14 and shrinks again from 15 to 20 atoms, in accordance with jellium model results.