Hhmmm. A method which uses a model to calculate a diffraction pattern which is
compared with observed data and the difference minimised by refining some
parameters. Then restarting the process by randomly shuffling some parameters.
I propose RRWAS - Rietveld Refinement With Atom Shuffling. Or maybe this is
what you would define as a "bad joke".
Cheers
o----------------------------oo0oo----------------------------o
Ian Madsen
Honorary Fellow
CSIRO Mineral Resources Flagship
Private Bag 10, Clayton South 3169
Victoria, AUSTRALIA
Phone +61 3 9545 8785 direct
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Email ian.mad...@csiro.au
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________________________________________
From: rietveld_l-requ...@ill.fr [rietveld_l-requ...@ill.fr] on behalf of
Yaroslav Filinchuk UCL [yaroslav.filinc...@uclouvain.be]
Sent: Thursday, December 17, 2015 9:17 AM
To: Lubomir Smrcok
Cc: rietveld_l@ill.fr
Subject: Re: structure solution terminology
Hi Lubo,
if we speak of diffraction, we have a Fourier transformation, so we
are not 100% in the direct space with any structure solution method.
However, the "structure solution in direct space" does not attempt to
work in the reciprocal space - all the manipulations are done in the
direct space. Also, it does not attempt to address properly the phase
problem, which is defined in the reciprocal space, but is simply
trying to find a model "directly" in the direct space. There is even
no inverse FT calculated! So, it is the fair name, IMHO.
Best regards,
Yaroslav
Wednesday, December 16, 2015, 11:05:05 PM, you wrote:
> Hi,
> I feel I have a problem with terminology. What's the right nickname for
> the method of structure solution from powders, which instead of analyzing
> electron (nuclear) density shuffles atoms or molecules around a cell and
> compares experimental and calculated patterns ? It could be well used also
> for single crystal data, I know, but it is not routinely done (yet ?).
> I remember that colloquially used phrase "structure solution in direct
> space" woke me up several times during plenary lectures at several
> conferences. What are we having in direct space ? IMHO just electron
> (nuclear) density. Its FT is our diffractogram so that if we fit
> diffractogram, are we still in direct space ? Of course, reciprocal space
> is a pure math and diffracted beam is quite realistic (BTW, are
> there photons also in reciprocal space :-) ?). But in which space are we when
> doing any
> crystallographic calculation ? OK, OK, you know what I am asking ... no
> bad jokes, please.
> May I ask for your 2 cents ?
> Thanks,
> Lubo
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