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Re: proposal for valence items



Dear David,

> The ball is in your court.
  
  You remember that I wanted to include textural items in the core CIF
for definitions of terms. A typical item would be:  

  Chirality:  The geometric property of a rigid object (or spatial
arrangement of points or atoms) of being nonsuperposable on its mirror
image; such an object has no symmetry operations of the second kind (a
mirror plane, m; a centre of inversion, -1; a roto-inversion axis, -N).
If the object is superposable on its mirror image, the object is
described as being achiral.

  I just had sufficient time before my recent trip to Chester to try and
put the definitions into 'CIF format'. I discovered that I did not know
how to do it and could not manage to work out how it should be done. I
thought this was probably because I was in too much of a rush. In
Chester I asked for advice from Brian and he told me that he thinks that
it is not possible to do this within the CIF rules. We are both
convinced that a glossary of crystallographic terms in electronic form
is an interesting and valid project but that the way to proceed is not
by use of CIF.

  So that seems to be the end of the matter as far as CIF and coredmg is
concerned. 

Best wishes,
  Howard 

-- 
Howard Flack        http://www.unige.ch/crystal/ahdf/Howard.Flack.html
Laboratoire de Cristallographie               Phone: 41 (22) 702 62 49
24 quai Ernest-Ansermet             mailto:Howard.Flack@cryst.unige.ch
CH-1211 Geneva 4, Switzerland                   Fax: 41 (22) 702 61 08

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