Total scattering and the pair distribution function in crystallography

The importance of total scattering and its Fourier transform, the pair distribution function, in crystallography was understood soon after it was shown that crystals diffract X-rays. However for the next fifty years or so other techniques based more firmly on the crystal lattice came to the fore and total scattering measurements were largely the domain of those studying liquid and amorphous structure. In the late 1980s it was ‘rediscovered’ as a way to uncover disorder within crystal structures and since then the combination of improved instrumentation and analysis has led to a resurgence of the total scattering method. This review sets out this journey, highlighting both the early origins and – more importantly – the ways that total scattering and pair distribution functions are routinely used within crystallography today.