Electronic shell structure of simple metal heteroclusters

By studying two small heteroclusters, ${\mathrm{Na}}_6$Mg and ${\mathrm{Na}}_8$Mg, we propose that the electronic shell structure which was previously observed in pure alkali-metal clusters should also exist in an alkali-metal cluster with a single divalent atom such as Mg. The calculations are performed self-consistently using pseudopotentials within the local-density approximation. We find that the charge distribution is delocalized with no evidence for directional bonding. A central Mg in a Na cluster primarily affects the s states and thus slightly modifies the set of shell closing numbers.