The structure of molten ZnCl2 and MgCl2

The structures of molten MgCl2 and ZnCl2 have been modelled using the reverse Monte Carlo method, based on neutron and x-ray diffraction data. We show that, although the structures are similar in terms of two-body correlations (e.g. partial radial distribution functions, average coordination numbers), there are important differences in the higher order correlations (e.g. bond angle and coordination number distributions). We have also analysed the models using bond-constraint counting. All of the results are consistent with the fact that ZnCl2 has a high viscosity and is a glass former (intermediate between strong and fragile), whereas MgCl2 is not a glass former, and with their different crystal structures.