Total scattering using synchrotron X-ray allows determining local and long-range structure of materials. Pair distribution function (PDF) is the Fourier transform of total scattering data, and it gives information on atomic distances and coordination numbers. PDF is especially useful in studying amorphous material. In my postdoctoral research, I have used PDF (differential-PDF specifically) to study the interactions at the interface of water-ferrihydrite. The strategy of using PDF usually involves fitting the data to a structural model. However, sometimes more advanced approaches, such as reverse monte carlo (RMC) simulations are needed to find the best structural model.