Analysis of Diffuse Scattering via the Reverse Monte Carlo Technique: a Systematic Investigation

The viability of using the reverse Monte Carlo (RMC) method for quantitative analysis of the diffuse X-ray or neutron scattering from single crystals of disordered materials is investigated. The method has been applied to a number of two- and three-dimensional model examples in which both occupational and displacement disorder are present separately and in combination. While occupational or displacement disorder are each separately handled well, with the RMC simulation reproducing the input correlation structure of the models quite effectively, more difficulty was encountered when the different types of disorder were present in combination. In this case, it was necessary to employ a strategy where the occupation shifts and displacement shifts were carried out alternately with no more than 10% of the crystal being visited before switching between the two modes. It was also found to be advantageous to exclude all high-angle diffraction data when assessing occupation shifts. Furthermore, a new method of modelling distortions by swapping the displacements of two atom sites rather than shifting each atom individually was found to produce chemically more realistic bond-length distributions.