Structural changes induced by an excess electron in small mercury clusters

Abstract

We discuss structural differences between neutral and negatively charged mercury clusters, with cluster sizes ranging from Hg 3 to Hg 7. We have optimized various types of structures for both species using quantum chemical ab initio methods. Because of the binding character of the p-type orbital occupied by the excess electron we observed a contraction of the bond length of approximately 0.2 Å on average. This corresponds to changes of the binding energy of the excess electron of 0.1 to 0.4 eV. In addition to this we encountered changes in the relative stability for different structures of the same cluster size by attaching an excess electron. The consequences for a meaningful comparison between theory and experiment are discussed in terms of recent measurements of electron affinities for mercury clusters. Finally, we propose a hybrid model for the incorporation of electron correlation effects. It consists of pairwise additive effective dispersion potentials and configuration interaction calculations that take into account correlation contributions originating from the excess electron. Numerical tests have been performed for selected clusters and revealed good agreement with more accurate ab initio methods.