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Comparative ab initio studies of small tin and lead clusters

We have performed ab initio total‐energy pseudopotential calculations on neutral and negatively charged Snn and Pbn (n = 3 − 10) clusters. The lowest energy structures have been determined for all clusters, and the stabilities of neutral clusters were investigated by comparing their evaporation energies and stability functions. Clusters with n = 7,10 were found to be most stable while the clusters with n = 8 and Pbs were much less stable, in agreement with features of the observed mass spectra. Calculations on Sn−n and Pb−n show that both atomic and electronic structures of a neutral cluster change substantially upon charging. The densities of states of Sn−n clusters reproduce the main features of the experimental photoelectron spectra. The agreement is poorer for Pb−n clusters where the calculations underestimate the separation between energy levels which we think is due to the larger spin‐orbit splitting in Pb, which was neglected in the calculations. We found that the differences between Sn and Pb clusters cannot be completely addressed without a more complete accounting of relativistic effects. The electron affinities of Snn and Pbn clusters have also been calculated and the results agree fairly well with experimental values. Finally we considered Sn2−4 and Pb2−4 clusters and related the results to the formation of Zintl anions in liquid alkali‐Sn and alkali‐Pb alloys.