HUCKEL MODEL AND EFFECTIVE-MEDIUM THEORY - GROUND-STATES FOR FCC AND ICOSAHEDRAL CLUSTERS

The ground state geometries are calculated for fee clusters with n les s than or equal to 100 and for icosahedral clusters with n less than o r equal to 77. The optimization is done by simulated annealing method. Only s-electrons are included in the Huckel model and the lattice rel axation is neglected. The Huckel model and the effective medium theory lead to different ground state geometries. The ground states favour i cosahedral structure when 18 less than or equal to n less than or equa l to 30 and fee lattice structure when 41 less than or equal to n less than or equal to 77.