When working with low-resolution datasets (especially those with very few reflections), some non-default options might be necessary to process the data with autoPROC. It is also often necessary to run some additional steps by hand, ie. taking the initial, autoPROC-generated files as a starting point for more fine-tuning.

Here we will collect some recipes for dealing with such datasets.

Start with defaults

The first assumption is, that a dataset can be processed with all defaults, ie. in the same way a high-resolution dataset from the same beamline/instrument and shift would be processed. Of course, this might include some parameter settings defining beam centre convention etc, but nothing specific to a low-resolution dataset.

Even if that run terminates without error, some checks should be done:

  • does it find a sensible cell and spacegroup?
  • do the parameters refine to expected values? Especially: does the distance and beam-centre stay close to the starting values? The plots distance.png and detector_center_origin.png can be used to check this:
    • we would expect the distance to stay within 1-2 mm of the starting value
    • the detector origin (and beam centre) should have stable values and not change more than say 10-20 pixels
    • those values obviously depend a lot on the stability of the beamline/instrument and the particular setup/alignment

If an autoPROC run terminates with an error or some of the above criteria are not met, the following sections will show some possible actions one could take.

Some useful macros and settings

A good set of options is to run with

% process -M LowResOrTricky ...

since this will set a few parameters typical for low-res (or any other more challenging) dataset. See output of process -M show what parameters this macro sets.

If the cell and/or spacegroup is known, running with

% process cell="40 50 60 90 90 90" symm=P21212 ...

can help XDS to find the correct indexing solution.

It is also a good idea to restrict the processing to the resolution where there actually are some reflections, eg by giving a resolution limit

% process -R 100.0 3.2 ...

or by specifying the detector edge via

% process autoPROC_XdsKeyword_TRUSTED_REGION="0.0 1.05" ...