Charge transfer mechanism in Cu-doped silicon clusters: a density functional study

Abstract

The geometric and bonding properties of Si n Cu ( n=4, 6) clusters were studied using the ab initio and density functional methods. Three isomers for Si 4Cu and two isomers for Si 6Cu were found. The structure of the most stable isomer for Si n Cu keeps the framework of corresponding Si n cluster nearly unchanged. Charge transfer in Si n Cu was examined to proceed from Cu to Si atoms. Population analysis indicates that the 3d shell of Cu atom is only slightly disturbed in Si n Cu and that Cu behaves like an alkali metal atom. The bonding nature in Si n Cu was analyzed by correlating the HOMO of Si n Cu to the LUMO of corresponding Si n cluster, and a dominant s–p or p–p bonding as well as a weak d–p bonding was found for the Cu–Si interaction in Si n Cu. This bonding nature is quite different from the interaction of 3d metals on silicon surfaces or 3d impurities in bulk silicon, where the bonding involving Si 3p and M 3d overlap is dominant. Remarkable similarity is found both in the geometry and in the bonding nature between the corresponding isomers of Si n Cu and Si n Na, confirming the alkali-metal-like behavior of Cu in Si n Cu.