Ulrich Baumann schrieb:
It is a known feature that data sets integrated with previous XDS
versions had frequently cumulative intensity distributions that could be
interpreted as twinning, i.e. the number of weak reflections was too
small and the curves for the acentric reflections had a sigmoidal shape.
This phenomenon also occured in my experience with data sets that had no
overlapping reflections as judged by integration with HKL2000 or MOSFLM
(where the intensity distributions then looked perfectly normal). From a
preliminary test, the December 2007 release of XDS appears to have
changed in this repect. When integrating the same data sets with a
previous version (I think August 2007) and this newest version, the
intensity dsitribution obtained by the latter looks now as expected.
Unfortunately there is no hint in the release notes.
As said, this is just my first impression and I would be curios if
otherpeople obeserve the same.
I observed the same, in numerous tests.
By the way, I think a part of the problem may also arise that CORRECT or
XSCALE apply too many correction factors -- try CORRECTIONS=DECAY only.
Gives worse R-factors and worse I/sig(I) but sometimes nicer intesity
distributions.
Sorry, have to disagree. Just look at e.g. MODPIX.pck and you know why
the MODULATION correction is needed. The detectors are unfortunately not
ideal.
Or use pointless on the INTEGRATE.HKL file (not XDS_ASCII.HKL) and then
SCALA -- we had one SAD case where this aided structure solution
significantly, just beware that the unit cell is not postrefined by the
CORRECT step then.
Ulrich
On Thu, 21 Feb 2008 19:24:32 +0100, George M. Sheldrick
<[EMAIL PROTECTED]> wrote:
All SHELX programs and XPREP are also indifferent to the asu choice
and to whether the data have been merged or not (even SHELX-76). It
is CCP4 historical baggage and high time it was eliminated.
On the official thread of this discussion, my impression is that 3D
integration programs (like XDS) are able to handle overlapping
reflections better than 2D integration programs, as one would expect.
One simple test is the mean value of |E^2-1|; if is is too small,
you either have twinning or reflection overlap. Unfortunately and
surprisingly XDS often fails this test (especially if the data have
been flattened with XSCALE),
George
On Thu, 21 Feb 2008, Peter Zwart wrote:
<vloeken in de kerk>
or use phenix, which is indifferent to format and asu choice.
</vloeken in de kerk>
P
Prof. George M. Sheldrick FRS
Dept. Structural Chemistry,
University of Goettingen,
Tammannstr. 4,
D37077 Goettingen, Germany
Tel. +49-551-39-3021 or -3068
Fax. +49-551-39-2582
