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Indexing

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Indexing, the derivation of unit cell parameters from given peak positions in a powder diffraction pattern, is a mandatory step in crystal structure solution from powder diffraction data. Knowing the unit cell can also be very useful in phase identification, considering that cell parameters can be used as restraints.

Match! can use two of the most prominent programs for indexing: Treor90 and Dicvol. All that is required to run an indexing calculation are either experimental peaks or raw diffraction data. If only raw (profile) but no peak data are present, Match! will automatically execute the raw data processing before the actual indexing calculation is started.

Before running the "Indexing" command, you should mark the peaks to be taken into account in the indexing calculation. If you do not mark any peaks, Match! will automatically use the 20 strongest peaks (if present) that are not yet covered by selected phases for indexing.

Once you have run the indexing command and maybe selected an indexing program, a parameter settings dialog will be displayed. Afterwards, the indexing calculation will be run.

When the calculation has finished successfully, you will be presented with one (or even a table of) potential solution(s). After accepting one (or more) solution(s), you will be taken to the “Indexing results” dialog (see below) where you can evaluate the solutions (i.e. unit cells), inspect peak data, select crystal system and space group (or let Match! or Dicvol do so automatically), and maybe add the solution as a new manual entry to the match list (e.g. to proceed with structure solution).

Screen shot displaying the dialog in which the indexing results can be examined.

Go to Match! Features Overview...
Previous: Rietveld refinement...
Next: Crystal structure solution using Endeavour...