Monte Carlo Analysis of Neutron Diffuse Scattering Data

Full text: This paper presents a discussion of a technique developed for the analysis and structural refinement of neutron diffuse scattering data. The technique involves processing the data into reciprocal space sections and modelling the diffuse scattering apparent in these sections. A Monte Carlo modelling approach is used in which the crystal energy is a function of interatomic distances between molecules and torsional rotations within molecules. The parameters of the model are the spring constants governing the interactions, as they determine the correlations which evolve when the model crystal structure is relaxed at finite temperature. When the model crystal has reached equilibrium its diffraction pattern is calculated by a second program and a third program is used to perform a χ2 goodness-of-fit test between observed and calculated data slices. This allows a least-squares routine to be used to refine the fit parameters and so automated refinement can proceed. The first application of this methodology to neutron, rather than X-ray, data is outlined. The sample studied was deuterated benzil, d-benzil, C14D10O2, for which data was collected using time-of-flight Laue diffraction on SXD at ISIS. (authors)