Realistic hybrid model for correlation effects in mercury clusters

We propose a simple hybrid model for the description of the effect of electron correlation on the structures of small- and medium-sized mercury clusters. The model represents a modification of the Hartree-Fock method augmented by pairwise dispersion interactions between the atoms derived from very accurate calculations for the dimer. We observe a quantitative agreement for the cohesive energies obtained from our model and quantum Monte Carlo calculations. The analysis of local atomic charge fluctuations shows that the covalent character of chemical bonding is only weakly affected by electron correlation in agreement with the basic assumption of our model. A sequence of structures up to Hg₅₅ following an icosahedral growth pattern appeared to be the most stable. The corresponding vertical ionization potentials are in good agreement with experiment, especially the shoulder around Hg₁₃ has been reproduced in our calculations.