Dear Mohamed,

more important than the absolute values of CCall/CCweak is the distribution of these statistics among the solution-trials of one SHELXD computation job (i.e. based on a particular data set).

In the HKL2MAP scatter-plot, there should be at least one, or a set of, solutions that are clearly separate in both CCall and CCweak from the bulk of trials - representing a bimodal distribution. Importantly, the best solution is promising if it is maximal in *both* CCall and CCweak. On the contrary, to my experience, two "best" solutions that are apart from the rest, but one maximal in CCall and the other in CCweak, point at the presence of not-completely-wrong, but incomplete substructures (in terms of correct sites).

Absolute "threshold values" for CC are hard to define, since these statistics depend on various factors, among these importantly the data resolution. But with all caution and no guarantee, I would start to call SAD solution trials "promising", if their CFOM = CCall + CCweak exceeds 30%.

Best wishes

Dear all

I am trying to solve a structure using Fe SAD collected with mini-kappa from several 
non-isomorphic crystals (following on from the previous 
 Xtriage suggests weak anomalous signal to 4 A.

For the SHELX pipeline using hkl2map, are there any metrics/numbers that I can 
use to judge the quality of each dataset? For example, what should be the value 
of CCall/CCweak to decide between strong/promising and useless cases?

Is there any difference between using CRANK2 and hkl2map, considering that the 
underlying software are the same?

Will the wavy Rmerge affect the 'solvability'?


Dr. rer. nat. Fabio Dall'Antonia
European Molecular Biology Laboratory c/o DESY
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D-22607 Hamburg

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