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Dear Mohamed,
the keyword "Friedel's_law" sets whether or not Friedel pairs are considered
equivalent for scaling.
As Kay Diederichs describes (e.g. on the xds wiki), there are cases where
assuming Friedel's law=true can lead to rejections in case there are strong
Bijvoet differences.
In many cases, this is not the case, and using Friedel's law=true has the
advantage that you get about twice as many reflections for scaling. That's
often an important gain for data quality, and you don't loose the anomalous
signal (because scaling algorithms are careful).
Try both Friedel's law=true and Friedel's law=false and read CORRECT.LP or
XSCALE.LP to see if you get many outlier rejections with the former. If not,
keep Friedel's law=true.
Best,
Tim
On Tuesday, October 20, 2015 03:52:22 PM Mohamed Noor wrote:
> Dear all
>
> I have a low-resolution dataset to about 4.2 A processed with XDS. As all
> three of the CHI2-VALUE OF FIT OF CORRECTION FACTORS values were about 1.4,
> I processed the images assuming Friedel's law=false and
> STRICT_ABSORPTION_CORRECTION=TRUE. However, using Xtriage, the anomalous
> signal seems to only extend to about 12 A at the most. So, I have two
> questions:
>
> 1. Can I process it by assuming Friedel's law=true?
>
> 2. How can I know where the signal comes from? The protein contains Fe
> (about 11 atoms) and the dataset was not collected at the absorption edge?
> In fact, the structure could/should be solvable using molecular replacement
> and I don't intend to do experimental phasing.
>
> I can post the processing stats if necessary. Thanks.
>
> Mohamed
- --
- --
Paul Scherrer Institut
Tim Gruene
- - persoenlich -
OFLC/102
CH-5232 Villigen PSI
phone: +41 (0)56 310 5754
GPG Key ID = A46BEE1A
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