Disordered or ‘glassy’ materials are of significant technological value. Their structure can be investigated by diffraction (neutron, X-ray, electron) techniques. When the available volume is very small (eg thin films, non-homogeneous structures) only electrons are suitable. Cockayne and McKenzie developed a technique of RDF analysis using energy filtered electron diffraction which gives information on structures of amorphous materials through the reduced intensity function ϕ(s) and the reduced density function G(r). This technique has been applied successfully to many systems.
A major limitation to the use of G(r) for characterisation of amorphous materials arises from the fact that, for electron diffraction, the G(r) measured is a combination of all partial radial distribution functions for each species in the solid. In addition, in practice there are many different models which will equally well fit the data. In order to overcome these difficulties, refinement needs to be done using a realistic starting atomic configuration. For this reason, we have produced starting models using ab-initio molecular dynamics (Car-Parrinello scheme).