<i>F</i>_<i>N</i>: A criterion for rating powder diffraction patterns and evaluating the reliability of powder-pattern indexing

TLDR

Over 30,000 powder diffraction patterns are currently available as references. The study proposes assigning quantitative quality factors to both existing and newly submitted powder diffraction patterns. The authors provide guidelines for using and implementing the FN rating system for powder diffraction patterns. The authors derived the FN figure of merit, which rapidly evaluates powder patterns, assesses reliability of powder‑derived units, and outperforms de Wolff's M20, leading to a recommendation to discontinue M20 for ranking.

Abstract

At present, over 30 000 powder diffraction patterns are available as references. It is proposed that the patterns on file as well as new patterns submitted for publication be assigned quantitative quality factors. A simple-to-use figure of merit, FN, covering both accuracy in the measurement of the positions of the diffraction lines and completeness of the pattern, has been derived: FN = (1/|{\bar \Delta 2 \theta}|) (N/Nposs), where Nposs is the number of independent diffraction lines possible up to the Nth observed line and |{\bar \Delta 2 \theta}| is the average absolute discrepancy between observed and calculated 2θ values. This figure of merit provides a rapid evaluation of powder patterns, in much the same way as the R factor provides a rating for single-crystal structure determinations. This figure of merit also provides a means to assess the reliability of a unit derived solely from powder data. At present FN ranking scheme is shown to be superior to de Wolff's M20 for ranking patterns. It is recommended that use of the latter be discontinued for that purpose. Guidelines are given on the use and implementation of the FN rating of powder diffraction patterns.