COVALENT EFFECTS IN IONIC SYSTEMS

Many materials which might be thought 'ionic', on the basis of the ele ctronegativity difference between the elements involved, exhibit non-i onic (or 'covalent') structural features. Electronic structure investi gations reveal the key concept that the properties of ions and their i nteractions are crucially influenced by their local coordination envir onment and that this gives a many-body character to the interionic for ces. Simulations with suitable interaction models show that a wide ran ge of 'covalent' behaviour may be accurately recovered within an ionic model.