[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [sdpd] model based structure refinement

hello
can i make the conclusion of this discussion as
"by knowing the exact lattice parameters and space group of sample, i should first expract the structure factors by FULLPROF and obtain the output files of SHELX format(.hkl and .ins files).After that i should solve the structure by SHELXS and refine the sturucture by SHELXL using WinGX "




________________________________
From: Armel Le Bail <armel.le_bail...@univ-lemans.fr>
To: sdpd...@yahoogroups.com
Sent: Wednesday, August 26, 2009 12:42:31 AM
Subject: Re: [sdpd] model based structure refinement

  
Hello,

Unless you have single crystals, the best approach is to use
powder diffraction data and to refine the model by using the
Rietveld method (FULLPROF, GSAS). If the cell parameters of
the model are close to those of the actual compound, you can
try to apply the atomic coordinates of the model and refine directly.
Otherwise you must first either index the pattern or refine the cell
parameters by using a software like CELREF. This because
the Rietveld method needs for a model already very close
to the final structure.

Be careful about preferred orientation which is frequently
a problem with powder data : the data recording should be
made carefully, the best being two times (one by pressing
the sample and one by dusting the sample one the sample
holder through a sieve - unless you use a capillary which
in general allows for avoiding preferred orientation) .

See for instance the SDPD Internet Course :
http://sdpd. univ-lemans. fr/DU-SDPD/
(free now, but without help and without diploma...)

Best wishes,

Armel Le Bail

At 23:44 25/08/2009 -0700, you wrote:
>dear sir
>if the sufficient knowledge about the structure is known(eg.. lattice 
>parameters, space group, approximate atomic positions etc), then what must 
>be the stategy to solve similar structures.
>
>i m working on soft ferrites which have spinel structureand space group Fd-3m.
>
>i have made a lot of literature survey, but i cannot find the proper 
>guidance about it
>
>thanks in anticipation





      

[Non-text portions of this message have been removed]



------------------------------------

Yahoo! Groups Links

<*> To visit your group on the web, go to:
    http://groups.yahoo.com/group/sdpd/

<*> Your email settings:
    Individual Email | Traditional

<*> To change settings online go to:
    http://groups.yahoo.com/group/sdpd/join
    (Yahoo! ID required)

<*> To change settings via email:
    mailto:sdpd-digest...@yahoogroups.com 
    mailto:sdpd-fullfeatured...@yahoogroups.com

<*> To unsubscribe from this group, send an email to:
    sdpd-unsubscribe...@yahoogroups.com

<*> Your use of Yahoo! Groups is subject to:
    http://docs.yahoo.com/info/terms/