Re: [sdpd] Best Cell?

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

> I wish to know what are criteria for 
> verifying the best cell suggested by 
> autoindexing. Especially, when there 
> are cells with V, 2V, 4V.

Going via a graphical button pushing route
to help you select good cells:

One suggestion which may help is to make use
of the latest bleeding edge beta test of 
the Chekcell for Windows program:

  http://www.ccp14.ac.uk/ccp/web-mirrors/lmgp-laugier-bochu/bleeding_edge_beta_versions/chekcell.zip

The standard Chekcell uses "parsimony of extra"
reflections on all available cell and spacegroup
combinations as a selection criteria of useful
cells that could potentially be the "best cell".

The latest beta version also links
into LePage (using ported source code originally written 
by A.L. Spek and A. Meetsma) which suggests sub
and super cells that can be checked via 
"parsimony of extra" plus gives the true
"reduced" cell.  This (plus the enhanced Truecell
feature) can help get around the bias of indexing
programs to suggest low symmetry, low volume cells.

Many indexing programs do not reliably give
the "reduced" cell as they are based on the 
Delaunay reduction. 

Refer:
  http://www.ccp14.ac.uk/solution/indexing/reduced_cell.html

-----------

Check cell tutorials (now slightly out of date) are at:
  http://www.ccp14.ac.uk/tutorial/lmgp/#chekcell

Another new feature is a GUI based cell transformation
option similar to the WinGX transformation interface.
With this you can be performing common point and
click cell transformations (Hexagonal to Rhombohedral -
Obverse/Reverse, etc) as well as manually defining the
transformation matrix.

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


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