Re: [sdpd] Automatic peak position hunting

["L. Cranswick" <L.M.D.Cranswick...@dl.ac.uk>]

> Yes, this occurs for a synchrotron powder pattern
> already discussed at this mailing list about indexing, in email :
> http://www.egroups.com/message/sdpd/113
> with a link to a compressed file containing the data :
> http://www.cristal.org/sdpd/indexrr.zip
> with name biesrf.*
> 
> The two not separable peaks are close to 4.2°(2-theta).
> 
> I think that, owing to the small FWHM, the step (0.01°2-theta) is 
> too large for the derivative method working well. 
> 
> Going to a 0.005° step, by adding intensities by a simple
> interpolation, makes that the 2 adjacent peaks are then located 
> by the automatic hunting without problem. 
> 
> Anyway, these peak hunting methods really cannot see 2 peaks 
> if their maximum are only separated by one step, even if the valley
> is deep. This was noticed by the 13th (unlucky ?) student 
> subscribing to the SDPD Internet  Course (and note that the email 
> number above is 113 ;-).

Thus the problem is not with the software programs 
but with the data collection conditions being
inappropriate - and then blaming the analysis software
as a substitute for proper recollection of the
data (?)

What would your course normally advise when non-optimal
data is collected?

Lachlan.

PS:  Is this cell still considered to be unsolved?

-- 
Lachlan M. D. Cranswick

Collaborative Computational Project No 14 (CCP14)
    for Single Crystal and Powder Diffraction
Daresbury Laboratory, Warrington, WA4 4AD U.K
Tel: +44-1925-603703  Fax: +44-1925-603124
E-mail: l.cranswick...@dl.ac.uk  Ext: 3703  Room C14
                           http://www.ccp14.ac.uk


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