Stability ofNanPb (n⩽7) clusters: A first-principles molecular-dynamics study

The structural and electronic properties of bimetallic clusters ${\mathrm{Na}}_{\mathit{n}}$Pb (n≤7) are calculated by means of a first-principles molecular-dynamics simulated annealing, using the local-density approximation and the pseudopotential plane-wave method. We obtain that the observed exceptional abundance of ${\mathrm{Na}}_6$Pb in molecular beams is due to the combination of electronic and geometrical factors, which are absent in the case of n≠6 clusters. In particular, we find that adding another Na atom to ${\mathrm{Na}}_6$Pb is energetically less favorable than adding it to a pure Na cluster, in contrast to what we obtain for smaller ${\mathrm{Na}}_{\mathit{n}}$Pb clusters. © 1996 The American Physical Society.