Analysis of Single-Crystal Diffuse X-Ray Scattering via Automatic Refinement of a Monte Carlo Model

Abstract

In this paper, the feasibility of automatic least-squares re®nement of a Monte Carlo model of a disordered structure by quantitative comparison of its calculated diffraction pattern with observed diffuse scattering data is demonstrated. At each stage of the re®nement, the goodness-of ®t parameter 1 2 is used as a quantitative measure of the agreement of the model with the observed data. Numerical estimates of the differentials of 1 2 with respect to the model parameters are calculated and these are used to provide automatic updating of the parameters via a least-squares algorithm. The method has been applied to the material Fe 3 (CO) 12 which shows strong diffuse scattering caused by the fact that the triangular Fe 3 group can occupy a given molecular site, in either of two different orientations. A model has been re®ned involving 16 independent parameters that describe both the correlation of neighbouring occupancy variables and local orientational and centre-of-mass translational relaxation displacements. Although the method still presents a formidable computational task even for the fastest of modern computers, the work described represents a signi®cant ®rst step towards the ultimate goal of allowing routine analysis of diffuse scattering data.

Diffuse scattering and local structure modeling in ferroelectrics

“…(1), such that atomic displacements representing the local modes are coupled. Parameters can be adjusted (also in an automated way [27]) until the experimental and calculated patterns agree. The advantage of this method is that it can be applied generally to all systems regardless of their complexity.…”

The three-dimensional pair distribution function analysis of disordered single crystals: basic concepts

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Evaluation of General and Tailor Made Force Fields via X-ray Thermal Diffuse Scattering Using Molecular Dynamics and Monte Carlo Simulations of Crystalline Aspirin

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