Dear Lubomir,
I' afraid that I might not get exactly what you mean. Are you talking
about something you actually use or are you looking for a term on a
method that exists somewhere "out there" and that you would like to use
potentially?
Assuming the latter, the closest I could think of is not really a
structure solution method but rather a structure completion method - and
this one is called "grid search method". It was introduced by Baur and
Fischer (1986). We apply it to incomplete structure models in a Rietveld
program: we are shifting a dummy atom (of a selected element)
systematically through the unit cell (i.e., it is a direct space
method), at each new fixed position (x,y,z) we refine its SOF and the
phases's scale and calculate the R-values while fixing all other
parameters. Then two maps are created, one with R as function of (x,y,z)
and one with SOF(x,y,z). The best position (x,y,z) (if any) of the atom
shows up as the absolute maximum (or several equivalent maxima for
equivalent positions) in the SOF map while the R-map shows an absolute
minimum (or several equivalent ones) at the same (x,y,z) as for the
SOF-maximum. Clearly, the systematic grid search may be confined to any
subsection of the unit cell. Different from Fourier methods the grid
search method does not suffer from termination effects, however, it is
rather time consuming...
Sorry if this should not match what you are looking for, as it is for
structure completion only and it definitely would not work for structure
solution from scratch. Anyway, here is the original citation:
Baur, W.H. and Fischer, R.X. (1986) Recognition and treatment of
background problems in neutron powder diffraction refinements. In
C.S. Barrett, J.B. Cohen, J. Faber, R. Jenkins, D.E. Leyden, J.C.
Russ, and P.K. Predecki, Eds., Advances in X-ray Analysis, 29, p.
131–142. Plenum Publishing Corporation, New York.
Best regards,
Johannes
Am 17.12.2015 um 07:54 schrieb Lubomir Smrcok:
OK,
But I am sure that any deciphering is a systematic rather than a
random process. I can however agree that when such a systematic
process is fueled by drinks, some random mental leaps might play a role.
This fact, unfortunately, does not help in solving this terminology
problem - at least not here.
Regards,
Lubo
On Thu, 17 Dec 2015, Leonid Solovyov wrote:
What's the right nickname for the method of structure solution from
powders
In Russian we use an equivalent to 'structure decipher'.
Sometimes, however, this is really 'structure solution' when we apply
vodka in the process ;)
*******************************************************
Leonid A. Solovyov
Institute of Chemistry and Chemical Technology
660036, Akademgorodok 50/24, Krasnoyarsk, Russia
http://sites.google.com/site/solovyovleonid
*******************************************************
--------------------------------------------
On Thu, 12/17/15, Lubomir Smrcok <uachs...@savba.sk> wrote:
Subject: structure solution terminology
To: rietveld_l@ill.fr
Date: Thursday, December 17, 2015, 5:05 AM
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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