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Updated: May 17, 2026

Analyzing Melts and Fluids from Ab Initio Molecular Dynamics Simulations with the UMD Package
Published on: September 17, 2021
Analysing Friedel averages and differences
Simon Parsons1, Phillip Pattison, Howard D Flack
1School of Chemistry and Centre for Science at Extreme Conditions, University of Edinburgh, Edinburgh, Scotland. s.parsons@ed.ac.uk
Abstract:
Various practical applications of the average (A) and difference (D) of Friedel opposites are described. Techniques based on the resonant-scattering contribution to Friedel differences are applied to see whether a crystal is centrosymmetric or not, and to determine the point group of the crystal. For the validation of a structural study, plots of A(obs) against A(model), and D(obs) against D(model) are used extensively. Moreover, it is useful to display both plots on the same graph. Intensity measurements on a crystal of NaClO(3) were made at three different speeds, with two different radiations and two different diffractometers, and treated with two different software packages and four different absorption corrections. The evaluation of these numerous data sets reveals underlying deficiencies. For comparison, plots of A(obs) against A(model), and D(obs) against D(model) are presented for two centrosymmetric crystals.
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