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Crystal structure solution using Endeavour

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Our program Endeavour for crystal structure solution from powder diffraction data can be quickly accessed by Match! as follows:

Assume that you are observing a set of pronounced peaks in your Match! diffraction pattern that are not covered by any known/identified phase. One potential explanation for this would be that these peaks belong to a presumably unknown phase (or at least to a phase that is not present in your reference database yet).

In order to check this, you should first try to index these peaks. Once you have been successful und obtained a promising set of unit cell parameters, you can store the result (peak data and unit cell parameters) in a manual entry in the match list.

Another important information for crystal structure solution may be the space group: Before adding a solution as a new manual entry to the match list, you can ask Match! to determine potential space group candidates, by activating the checkbox “Use extinctions to restrict space grps.” in the “Crystal structure” section of the "Indexing results" dialog. Once you have done so, only space groups that agree with the observed peaks in the current experimental pattern are available in the “Space group” drop-down box. This function works by checking systematic absences. Dicvol normally also suggests a space group that will be used by Match! without additional user interaction.

If you are using Windows as your operating system, Match! can now forward the data you have collected (peak data, unit cell parameters and maybe space group) from the manual entry just mentioned to Endeavour and run it. In Endeavour, you can then run the so-called "Structure solution wizard" in order to setup the actual structure solution calculations. The only information that you still have to enter/add at this point is the composition of your compound, i.e. the unit cell contents. The background for this is as follows:

Endeavour uses a so-called “direct-space method”: It starts by placing the atoms at random positions in the unit cell and then moves them around, trying to minimize the R-factor (difference between experimental and calculated diffraction pattern) and the potential energy. For this, it needs to know which atoms (elements and maybe oxidation states/charges) are present in the unit cell. Hence, in order to be able to apply Endeavour, you should at least know the composition (formula sum or molecule structure) of the unknown compound, e.g. from XRF experiments or chemical analysis. In addition, you also need the number of formula units per unit cell (Z). Endeavour can help you with the latter if you have at least a rough idea of the density of the material and/or of the space filling percentage.

Once the structure solution calculations have finished and a promising structural model has been found, you can export the resulting crystal structure from Endeavour to a cif-file, and then re-import this into the manual entry just mentioned, e.g. in order to run a Rietveld refinement.

Go to Match! Features Overview...
Previous: Indexing...
Next: Runs on Mac, Linux and of course Windows...