Scandium fluoride has recently been identified as a very simple example of a material showing negative thermal expansion over a wide range of temperatures. In particular, it might be thought to illustrate the classic mechanism of thermally excited octahedral rotations causing shrinkage of the crystal on heating. However, recent work has suggested that the dynamics are much more anharmonic than suggested by this picture. We are proposing a total scattering experiment, with results to be analysed by the Reverse Monte Carlo method. Previous successes with this method on perovskites suggest that this approach should be capable of giving a good structural understanding of the processes that lead to negative thermal expansion.