'Covalent' effects in 'ionic' systems

Many materials which might be thought 'ionic', on the basis of the electronegativity difference between the elements involved, exhibit non-ionic (or 'covalent') structural features. Electronic structure investigations reveal the key concept that the properties of ions and their interactions are crucially influenced by their local coordination environment and that this gives a many-body character to the interionic forces. Simulations with suitable interaction models show that a wide range of 'covalent' behaviour may be accurately recovered within an ionic model.