Electronic shell structure in large metal clusters

Abstract

This thesis reviews six publications which investigate the effect of the surface on the electronic shell structure in large metal clusters. The Hückel model is used to study the shell structure and cluster geometry of fee clusters. A tight binding model and the Monte Carlo technique is used to simulate metallic fee clusters at finite temperatures for determining the level spacing distribution at the Fermi energy. A potential-well approximation is used to study the shell structure in cuboctahedral and icosahedral clusters and also to calculate the band structure in cluster-assembled materials. The Woods-Saxon potential has been used to study the effect of the softness of the surface potential on the shell structure. The main results are as follows: (i) The surface faceting destroys the shell structure in fee clusters already when the cluster has of the order of 100 atoms. (ii) The icosahedral clusters have the same shell structure as the sphere up to about 1000 atoms. (iii) The surface roughness causes the level distribution to be a Wigner distribution. (iv) Using the Woods-Saxon potential a softness can be found where the shell structure is governed by the classical star orbit. However, real metal clusters are not soft enough to exhibit the signature of the star orbit. (v) If crystalline materials can be formed from magic metal clusters, they are expected to be semiconductors.