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Re: Absolute structure



Following my request, Brian has signed up George Sheldrick on the
coredmg list. He has accepted and is now receiving the coredmg mailings.
I copy parts of his acceptance e-mail below so that it appears in the
archive of coredmg at a suitable place. Unfortunately George's cc of
this message went to one of my old e-mail addresses and I only found the
message a few days ago.

In a few moments I'll send some more thoughts on counting Friedels.

> 
> Brian McMahon wrote:
> > 
> > Dear George
> > 
> > Howard has requested that I add you to the coreDMG discussion list of
> > COMCIFS, as he has something he wishes you to hear (I'm not sure whether
> > this is good news or bad!).
> > 
> > I have taken the liberty of adding you to the mailing list - I hope you
> > don't mind.
> > 
> > Best wishes
> > Brian
> > 

> > Forwarded message:
> > > From Howard.Flack@cryst.unige.ch Wed Jan 14 10:54 GMT 1998

> > >
> > > Dear David and Brian,
> > >>
> > >> D80.3 Extent of measured data
> > >> -----------------------------
> > >
> > >   I intend to contribute to this item and to the Friedel count question
> > > again but as George has ideas on this, it would be most helpful if he
> > > could be added or add himself to the coredmg list.
> ========================================================================
> 
> Dear Brian
> 
>  ...............   removed by HDF
>
>  For the
> completeness calculation, in my current programs I combined Friedel
> opposites for this purpose both in the measured and in the theoretically
> measurable categories, i.e. one could obtain 100% completeness by only
> measuring at least one of each Friedel pair.  I decided that this
> approach would create the least confusion amongst contributors and
> editors.  I agree (with the comment that I think Howard is going to
> make!) that it would be better to define two measures of completeness
> for non-centrosymmetric structures, one with the Friedel opposites
> combined and the other with them treated as independent.  However it's
> too late now, the next chance to create more confusion is January 1999!
> All this goes to illustrate the desirability of letting COMCIFS comment
> on new CIF definitions BEFORE making them 'official' by publishing them
> in the 'Notes for Authors'.
> 
> Best wishes, George




-- 
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) 781 21 92


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