The procedure for deriving interatomic potentials for molecular ionic materials, using empirical fitting procedures, is described. Potentials are obtained for carbonates, phosphates and perchlorates, and used to calculate crystal and lattice properties which are compared with available experimental data.

Knowledge of the dynamic dimension of materials is an extremely important ingredient for understanding their properties. Neutron scattering is uniquely capable of revealing aspects of the atomic and molecular geometry of motions over a wide range of time scales. To illustrate this fact, we give a number of examples from different areas of materials science. We discuss the diffusion of hydrogen in protonic conductors; the hydration of portland cement; and aspects of the molecular rheology of polymers, emphasizing in particular the effect of branching. All of these experiments have added important basic information to the understanding of the respective systems. With the advent of the new megawatt neutron spallation sources, the role of neutron scattering in revealing the dynamical properties of materials is expected to increase substantially.