An ab initio investigation of structure and energetics of clusters MgnCl2n

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Abstract
Results of a systematic theoretical study of stoichiometric clusters MgnCl2n up to n=24 are reported within the self-consistent-field (SCF) approximation. Calculations within second-order Mo/ller–Plesset perturbation theory and single- and double-excitation coupled cluster method with a perturbational estimate of triples excitations are performed for the smaller clusters to check accuracies. The clusters MgnCl2n do not show a consistent preference for geometries which are fragments of the bulk lattice as it is known for the alkali halide systems: Small clusters MgnCl2n prefer linear chain structures corresponding to the SiS2 crystal lattice, the most stable medium sized clusters (5≤n<20) are high-symmetry ‘‘cyclic’’ SiS2 structures, and only for large systems (n≥20) we realize a transition to the magnesium chloride lattice structure. The computed binding energies of the larger clusters allow for an extrapolation of the lattice energy which is in good agreement with experiment.