Efficient fitting of single-crystal diffuse scattering in interaction space: a mean-field approach

Abstract

The diffraction patterns of crystalline materials with strongly correlated disorder are characterized by the presence of structured diffuse scattering. Conventional analysis approaches generally seek to interpret this scattering either atomistically or in terms of pairwise (Warren–Cowley) correlation parameters. Here it is demonstrated how a mean-field methodology allows efficient fitting of diffuse scattering directly in terms of a microscopic interaction model. In this way the approach gives as its output the underlying physics responsible for correlated disorder. Moreover, the use of a very small number of parameters during fitting renders the approach surprisingly robust to data incompleteness, a particular advantage when seeking to interpret single-crystal diffuse scattering measured in complex sample environments. As the basis of this proof-of-concept study, a toy model is used based on strongly correlated disorder in diammine mercury(II) halides.

Spinteract: a program to refine magnetic interactions to diffuse scattering data

“…Finally, the diffuse-scattering-based approach outlined here is not restricted to estimating interactions between magnetic degrees of freedom. By analysing the diffuse scattering from non-magnetic degrees of freedom, such orientationallydisordered molecular degrees of freedom in crystals, or shortrange chemical order in binary alloys, similar information about the underlying interactions may be determined from Xray or neutron scattering measurements [78].…”

Local structure and dynamics in MPt(CN)6 Prussian blue analogues

“…Consequently, we develop here a modified 'interaction-space' approach 28,29 for interpreting the PDFs of MPt(CN) 6 whereby we optimise the parameters of an intentionally simplistic empirical potential model so as to reproduce the experimentallydetermined pair correlations. In spirit our approach shares much in common with the empirical potential structure refinement (EPSR) methodology used to interpret the PDFs of heavily disordered materials such as liquids and glasses.…”

Local Structure and Dynamics in MPt(CN)6 Prussian Blue Analogues

“…Consequently, we develop here a modified “interaction-space” approach , for interpreting the PDFs of MPt­(CN) 6 whereby we optimize the parameters of an intentionally simplistic empirical potential model so as to reproduce the experimentally determined pair correlations. In spirit, our approach shares much in common with the empirical potential structure refinement methodology used to interpret the PDFs of heavily disordered materials such as liquids and glasses .…”