Theoretical study of the size dependence of ionization potential and electron affinity of metallic clusters

摘要

Ionization potentials (I) and electron affinities (A) of lithium clusters are studied by treating exchange effects exactly within the exchangehyphen;only densityhyphen;functional theory and employing the spherical jellium background model of metallic clusters. In the past, ionization potentials of metallic clusters have been studied by treating the exchange and correlation effects approximately via the local density approximation (LDA). We show that such a calculation leads to ionization potentials which, when extrapolated to large clusters, do not give the correct work functionWfor the bulk metal as they should. Furthermore, the LDA does not lead to convergent solutions for cluster anions of all sizes. Thus the electron affinities of these clusters cannot be studied within this approximation. On the other hand, by treating exchange effects exactly, solutions for negative ions can also be obtained. We demonstrate that both the ionization potentials and the electron affinities thus obtained extrapolate to the correct value of the work function for the bulk. Furthermore,IandAon the average vary with the size of the cluster asI=W+0.5/(R+a) andA=Wminus;0.5/(R+a), respectively, whereRis the radius of the cluster and lsquo;lsquo;arsquo;rsquo; is a microscopic distance.