On the bonding of small group 12 clusters

Characteristic properties as well as possible differences in bonding of small group 12 clusters Mn (M = Zn, Cd, Hg; n = 2, . . . , 6) have been investigated by quantum chemical ab initio methods, i.e., relativistic large-core pseudopotentials, core-polarization potentials and coupled-cluster correlation treatments. A comparison of cohesive energies and spectroscopic properties like ionization potentials, electron affinities, and vibrational frequencies reveals a close similarity between the clusters of Cd and Hg. For Zn clusters we observed an exceptional increase in stability between Zn3 and Zn4. In order to get a more qualitative picture of the covalent contributions to bonding we have calculated the electron localization function (ELF). The ELF analysis is in accordance with the calculated spectroscopic properties and shows predominant van der Waals interactions with weak covalent contributions for all the cluster sizes