Hi Uli, On Fri, Feb 22, 2008 at 09:53:36AM +0100, Ulrich Baumann wrote: > 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.
Absolutely: pre-December2007 releases had the tendency to give significant intensities for high resolution ranges where visual inspection of images didn't show any spots. This lead to sometimes over-optimisitic high-resolution data - the various statistics like Rmerge/Rmeas and I/sig(I) showed a kind of plateu towards high resolution. With the December2007 release this is gone and the statistics nicely explode towards high resolution and non-existent data - which is a very good thing, since structures are solved with real data and not through good I/sig(I) statistics. This also means that the intensity statistics are now clean and as expected. At least that's my impression. Clemens > 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. > 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 > > > > -- > Prof Ulrich Baumann > Departement für Chemie und Biochemie > Freiestrasse 3 > Ch-3012 Bern, Switzerland > phone + 41 (0)31 631 4320/4343 > fax + 41 (0) 31 631 4887 > -- *************************************************************** * Clemens Vonrhein, Ph.D. vonrhein AT GlobalPhasing DOT com * * Global Phasing Ltd. * Sheraton House, Castle Park * Cambridge CB3 0AX, UK *-------------------------------------------------------------- * BUSTER Development Group (http://www.globalphasing.com) ***************************************************************
