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Re: A DDLm problem


On Wed, 25 Feb 2009, David Brown wrote:
> POSSIBLE SOLUTIONS
> Tree 3 above can be made to work if the beta form can be made
> invisible.  It cannot be completely invisible as it must appear in the
> appropriate CIF dictionary, and its text description will be displayed
> by any CIF editor such as publCIF or enCIFer.
>
> One possible solution is to include a flag in the dictionary definition
> to indicate that the item should be hidden from the user or deleted
> after the calculation is complete.

I would tend towards this solution (1), but with multiple evaluation
strategies (i.e. loop_ed) combined with dREL software that that checks 
for multiple iterations around an evaluation path and which falls back 
to an alternative if it exists, as well as the flag to say don't print 
this in a result CIF (and possibly hide this in an editor!). 


> METHODS ARE THE NEW DEFINITIONS
> At the meeting of COMCIFS in Osaka it was decided that when a method is
> present in the dictionary it takes precedence over text in defining the
> item.  One immediate corollary to this is that only one method is
> allowed for each data item. 

I am not sure why that is a corollary.
Why is it not possible to have fallback methods when a particular 
evaluation strategy fails? 

My understanding of the derivation pathway was more like:

              U11,U22,...   B11,B22...
                /           /
 3    beta -> Uaniso -> Baniso 
                 \         \
                  Uiso       Biso

i.e. there are discrete component forms  as well as matrix forms 
as well as tensor forms. If I understand correctly, beta is the *only* 
true tensor form of the ADPs. If you want to convert between
different unit cells, transforming the Uijs is only possible by converting to 
tensor form before the symmetry transform and back to Uijs afterwards. 
To obfuscate its role in a definitive treatise seems lacking.
Of course I may be wrong :))

Also, for calculating H atom adp's isn't there an algorithm based on Uiso 
of their coordinating C,N,O atoms?
How are you going to get Uiso from Uaniso?


> I am looking for feed back.  However if I receive none, I will assume
> that you agree that unwanted intermediates should be hidden by giving
> them meaningless datanames and text definitions that conceal their content.
>
> Please circulate your thoughts on this problem to the whole discussion
> list.

$0.02
Doug
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