Structure and binding of molecular clusters of trivalent metal halides in an ionic model

A model of ionic interactions first proposed for the molecular monomers of alkaline earth dihalides (Galli, G. and Tosi, M.P., Nuovo Cimento D, 4 (1984) 413) is used in a systematic study of the structure and binding of monomeric and dimeric units of Al, Fe and Ga chlorides, bromides and iodides. Ionized states obtained by stripping or adding a halogen ion are considered in addition to neutral states. The main motivation for this work comes from recent studies of liquid structure in several of these systems by neutron and X-ray diffraction and Raman scattering. Main attention is consequently given in the present calculations to 1) bond lengths and bond angles in isolated clusters as precursors of local structures in melts, and 2) stability of local structures against fluctuations into ionized states. The results are discussed in comparison with the available experimental data as well as with the results from Hartree-Fock and density-functional calculations