Indexing

Basics

Within Match!, indexing means the derivation of unit cell parameters from given peak positions in a powder diffraction pattern. It is a more or less mandatory step in crystal structure solution from powder diffraction data, e.g. using Endeavour. Knowing the unit cell can also be very useful in phase identification, taking into account that cell parameters can be used as restraints.

Quite a lot of indexing programs are available today; Match! can use two of the most prominent: Treor90 and Dicvol.

Prerequisites

In principle, you can download and install Treor and/or Dicvol separately on your PC, however, these programs are also included in the FullProf Suite. Hence, there is no need to bother with this if you have already installed FullProf on your computer (e.g. for Rietveld refinement). Match! will automatically locate the Treor90 and Dicvol06 programs included in this package, so you are ready to setup and run indexing calculations straight away. If this does not apply, you should take a look at the indexing options, in order to learn how to setup the paths to the indexing programs.

Setting up and running indexing calculations

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 when the indexing command is run, 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.

You can run indexing either using the corresponding command from the "Tools" menu, or simply by pressing the corresponding button in the main toolbar. Depending on the current settings and situation, this will either bring up a dialog asking which indexing method (Treor or Dicvol) you would like to use, run the default indexing program, or display the table of indexing results that are already present (and from which also new calculations can be run).

Once you have run the indexing command and maybe selected an indexing program, the corresponding parameter settings dialog will be displayed. The available parameters are different for Treor and Dicvol, so please click on these links to get more information about the two programs and their parameters.

Results viewing

When the calculation has finished, you may be presented with one (or even a table of) potential solution(s). Please mark and/or confirm the solution(s) you would like to accept. You will then be taken to the indexing results dialog where you can evaluate the solutions (i.e. unit cells), inspect peak data, select crystal system and space group, and maybe add the solution as a new manual entry to the match list (e.g. in order to proceed with structure solution).

Please note: