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Re: [ccp4bb] XDS and overlaps
 

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CCP4bb <-- 2008 <-- February 2008 <-- 21 February 2008
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From: Edward Berry eaberry {- at -} LBL {- dot -} GOV
Date: 2008-02-21 		Next message:
Subject: Re: possible solutions for those troobleshooting ccp4 and ccp4i...
From: Johan Turkenburg jpt {- at -} YSBL {- dot -} YORK {- dot -} AC {- dot -} UK
Date: 2008-02-21


Subject: Re: XDS and overlaps
From: Engin Ozkan eozkan {- at -} STANFORD {- dot -} EDU
Date: 2008-02-21
In this case, XDS-processed data is clearly twinned, if one were to
believe moments and the cumulative intensity distribution calculated
by truncate (and everyone should - channelling Dr. Dodson).

Why I'm worried about XDS separating relatively overlapped spots is
the funny intensity stats that may result from this (as George
Sheldrick and Martin Hallberg has pointed out)? The incomplete
HKL2000-processed data (70%) still has intermediate values for the
intensity stats, leaning towards twinning. This somewhat agrees with
twinning, but not overzealous data integration.

Engin

P.S. If twinning (perfect in this case) is taken into account
structure refines to 20/26% R at 2.8 Ang., unlike in Martin's case.
Without twinning, numbers are 29/33%.

Quoting "George M. Sheldrick" :

> 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:
>
>>
>> or use phenix, which is indifferent to format and asu choice.
>>
>>
>> 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
>
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