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Re: CIF dicsussion on chemical structure

Thanks Peter for giving us a summary of what your software can do.  
While I agree entirely that in the first instance we should focus on 
finite molecules, I am anxious to ensure that the scheme we adopt does 
not preclude the further extension to infinite structures (which is what 
Discussion #6 aims to do) even if we do not wish to implement this in 
the first round.  I shall therefore be watching any proposals with that 
in mind.  In particular, supplying all the chemical information in the 
_atom_site loop may restrict our ability to expand to infinite 
structures, because the basis of the atom_site loop is the asymmetric 
unit which in general may bear little relation to the chemical units.

PMR wrote:
To accomplish this I this is valuable to be able to create additional 
annotation in the _atom_site table and to have atoms in there which do 
not, or cannot contribute to the diffraction (i.e. occupancy = 0.0) Does 
this look reasonable?

The dummy atom feature is already present in the current version of the 
core dictionary.

David Brown

fn:I.David Brown
org:McMaster University;Brockhouse Institute for Materials Research
adr:;;King St. W;Hamilton;Ontario;L8S 4M1;Canada
title:Professor Emeritus
tel;work:+905 525 9140 x 24710
tel;fax:+905 521 2773

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