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*To*:*Multiple recipients of list <coredmg@iucr.org>***Subject**:**Re: F(000)****From**:**Howard Flack <Howard.Flack@cryst.unige.ch>***Date*:*Thu, 19 Feb 1998 11:00:22 GMT**Reply-To*:*coredmg@iucr.org*

> > Please can you advise? > In any case it's no > longer a required item. As a calculated F(000) including dispersion is never used in any crystallographic calculation, I would recommend him not to include it in the CIF. If by any chance he has found a use for the dispersive F(000), I only hope he did not calculate it with: > > F(000) = [ sum (f~r~^2^ + f~i~^2^) ]^1/2^ because it should be: F(000) = [ (sum f~r~)^2^ + (sum f~i~)^2^ ]^1/2^ the sum being over each atom in the unit cell. Dispersion-free calculated F(000) is used in electron-density calculation by Fourier inversion. In this case it corresponds to the number of electrons in the unit cell which will be integral for stoichiometric compounds. I recommend coredmg to remove _exptl_crystal_F_000 from the dictionary as it is useless, ill-defined and causes more bother than it is worth. H. -- 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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