[sdpd] Are the following fair comments about present Rietveld limitations for SDPD?

[L.M.D.Cranswick...@dl.ac.uk]

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Sort of related to previous messages on Fourier Maps.

I am interested in some quality control with respect to some 
talk notes related to solving relatively complex organics from
powder diffraction data.

Armel mentioned in the 1998 No. 20 IUCr CPD newsletter
(pg 30) that "The new paradox is that we can locate now
molecules in much bigger cells than we could refine
without restraints".

Thus even if "routine" structure solution of organics was
possible, users would experience the bottleneck for obtaining
a publication quality elsewhere: e.g., powder indexing and 
structure refinement.

Thus would the following be considered as fair comments with
respect to the structure refinement "bottleneck"?


"Where Rietveld programs are "behind" compared to Single Crystal 
Refinement Suites.  (focussing on organic structures)"

1. Lack of routine Structure Visualization

2. Lack of user-friendly graphical building up of the structure (Q peak 
  finding - requiring appropriate algorithms for powder diffraction 
  such as "maximum entropy") 

3. Lack of user-friendly structure refinement by interacting with the 
  graphical structure on the screen

4. Lack of easy to use powerful point and click restraints and rigid 
  bodies. (restraints seem mandatory for refining relatively complex 
  organics from powder data).

5. Lack of easy to use Fourier Map Generation and viewing using appropriate 
  algorithms such as maximum entropy to clear up the electron density 
  contour maps.

6. Lack of automatic or "point and click" hydrogen placement and refinement 
  options.


Lachlan.

-- 
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