Reverse Monte Carlo Analysis of Powder Patterns

A Monte Carlo algorithm for the analysis of powder diffraction patterns is presented. One aim of this algorithm, which can be used as a supplement to the regular Rietveld refinement, is to provide a self-consistent determination of the thermal displacements of the atoms. This is achieved by modelling the total scattered intensity, comprising both the Bragg peak intensity and the diffuse contribution to the spectrum from the scattering density of an assembly of atoms. This assembly, which is constructed by the reverse Monte Carlo technique so as to yield a best fit with the data, is then used to calculate the average atomic thermal displacements. This allows for a refinement that, in principle, no longer requires angle-dependent background parameters, and that is well suited for dealing with highly anisotropic Debye-Waller factors and split atomic sites.