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Abstract
Computer simulation studies of molten salts and disordered ionic solids employing phenomenological ionic models have proved useful in helping to understand the structure of these systems and their structure-dependent properties. A minimal requirement on such models is that they should give a reasonable account of cohesion in crystals and in molecules and small clusters of these compounds, and in turn the analysis of cohesive and vibrational properties of ionic systems in solid and molecular states has helped to determine useful model interactions. For an introduction to these topics the author first reports from the work carried out in the 1980s with W. Andreoni and G. Galli on what is learnt in Hartree-Fock and configuration–interaction calculations on the neutral and ionized monomer and dimer of NaCl. Then the author recalls how a deformation-dipole model was built for the cohesion of the neutral alkali halide monomers by combining a classical multipolar expansion with a quantum overlap expansion, and how this model relates to the theory of the cohesion and the vibrational spectrum of the alkali halide crystals. Finally, the author illustrates some applications to molecules and microclusters of polyvalent metal halides, from work carried out with Z. Akdeniz and coworkers. Transferability of model parameters for the halogen ions between different compounds and different aggregation states is crucial for these applications, and is achieved in the deformation-dipole model.
Acknowledgments
It is a pleasure to express my gratitude to Fausto Fumi, Wanda Andreoni, Giulia Galli, and Zehra Akdeniz for all that I have learnt in collaborating with them. On this occasion I also wish to thank Wanda Andreoni and Giulia Galli for an unforgettable week of work on the NaCl molecule at the EPF–Lausanne.
Notes
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