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I looked to all the mails concerning your question and I would like to
clarify some points:<br>
First when you say that A and B occupy the same 10 positions. It means
that you have partial occupancies in the real structure, which exhibits
a symmetry controled by 2 levers (symetry constraints):<br>
- the size of the cell (translational symetry)<br>
- the space group (equivalent positions...). <br>
<br>
In order to model such a real system (which exhibits partial
occupancies or occupancy of a position by different elements and/or
vacancies), you should first break the symetry constraints, i.e. by
changing the dimension of the cell (change the translational symetry
contraints) and by changing the space group (from high symetry to
triclinic P1). <br>
<br>
If you properly generate such a supercell and impose P1 symetry then
you will have no more problems.<br>
<br>
In my case, I usually generate such a supercell using the following
strategy:<br>
- consideration of the experimental structure (small cell / high
symetry) in a visualization program such as Endeavour or Diamond<br>
- remove any partial occupancies<br>
- transformation of the structure into P1 (this could be easily done
with Endeavour or by hand)<br>
- generation of a supercell using an internal program or excel or any
program allowing to recalculate the new fractional coordinates<br>
- occupation of the previously equivalent sites (for translation or
space group symetry reasons) by A and B<br>
- save the so-obtained file in cif format <br>
- use the program cif2struct to generate a proper struct file<br>
<br>
However, such a strategy should be done only if you clearly understand
the chemistry and physics of the system you are investigated and the
way to achieve your goal without loosing to much time (use of a too big
supercell ...). <br>
<br>
Best Regards<br>
<br>
Xavier<br>
<br>
Ghosh SUDDHASATTWA a écrit :
<blockquote
cite="mid:!~!UENERkVCMDkAAQACAAAAAAAAAAAAAAAAABgAAAAAAAAAAKaM5WqTP0uhKD+WrdhOAsKAAAAQAAAAoyFJHpQz5EiiX9%2FX9QEWlgEAAAAA@igcar.gov.in"
type="cite">
<pre wrap="">Dear Dr.Marks, Dr.Stefaan, and Wien2k users,
I have tried hard to solve the problem but I have unfortunately not been
able to solve it.
The only problem is that both A and B occupy the same 10 positions(10
different) and the structure cannot be generated using the StructGen module.
That for using the supercell program requires a valid case.struct file.
Please help
Thanks in advance
Suddhasattwa Ghosh
-----Original Message-----
From: <a class="moz-txt-link-abbreviated" href="mailto:wien-bounces@zeus.theochem.tuwien.ac.at">wien-bounces@zeus.theochem.tuwien.ac.at</a>
[<a class="moz-txt-link-freetext" href="mailto:wien-bounces@zeus.theochem.tuwien.ac.at">mailto:wien-bounces@zeus.theochem.tuwien.ac.at</a>] On Behalf Of Gerhard Fecher
Sent: Tuesday, January 05, 2010 4:35 PM
To: A Mailing list for WIEN2k users
Subject: Re: [Wien] [Wien2k Users] Structure Generation of Solid
SolutioninWien2k
Hi Peter,
maybe one should mention that the CALPHAD journal (published by Elsevier)
might be a good source to learn about such calculations for alloys.
My remark was probably missing that I would not do it "that way" but
probably combine it with some knowledge
about statistics and - dependent on the problem I have in mind - with some
Monte Carlo algorithm.
(By the way, do you know about the progress of an ATAT-Wien2k interface,
last year it was not available ?)
Ciao
Gerhard
====================================
Dr. Gerhard H. Fecher
Institut of Inorganic and Analytical Chemistry
Johannes Gutenberg - University
55099 Mainz
________________________________________
Von: <a class="moz-txt-link-abbreviated" href="mailto:wien-bounces@zeus.theochem.tuwien.ac.at">wien-bounces@zeus.theochem.tuwien.ac.at</a>
[<a class="moz-txt-link-abbreviated" href="mailto:wien-bounces@zeus.theochem.tuwien.ac.at">wien-bounces@zeus.theochem.tuwien.ac.at</a>] im Auftrag von Peter Blaha
[<a class="moz-txt-link-abbreviated" href="mailto:pblaha@theochem.tuwien.ac.at">pblaha@theochem.tuwien.ac.at</a>]
Gesendet: Dienstag, 29. Dezember 2009 19:16
An: A Mailing list for WIEN2k users
Betreff: Re: [Wien] [Wien2k Users] Structure Generation of Solid
Solution inWien2k
Alloys are nowadays studied by the so-called "cluster expansion", where
the cluster interaction parameters are obtained from supercells with several
different configurations (you don't need "all" possible variations).
Even with medium sized supercells one can already learn a lot about
tendencies for clustering, ....
Gerhard Fecher schrieb:
</pre>
<blockquote type="cite">
<pre wrap="">First a question, how is the bandstructure defined in a random alloy when
</pre>
</blockquote>
<pre wrap=""><!---->the infinite periodicity is lost ?
</pre>
<blockquote type="cite">
<pre wrap="">To specify 60 % of the sites to be occupied by A, you need a supercell say
</pre>
</blockquote>
<pre wrap=""><!---->with 100 atoms and
</pre>
<blockquote type="cite">
<pre wrap="">to set 60 of the sites by A and 40 by B atoms (always one atom no fraction
</pre>
</blockquote>
<pre wrap=""><!---->!)
</pre>
<blockquote type="cite">
<pre wrap="">this you have to do for all distinguishable (!) permutations (use some
</pre>
</blockquote>
<pre wrap=""><!---->statistics !)
</pre>
<blockquote type="cite">
<pre wrap="">of the site occupations, as for example
1st: AAAAA-(60x)-AAAA BBBBB-(40x)-BBBBB
2nd: BAAAA-(59x)-AAAA ABBBB-(39x)-BBBBB
3rd: BBAAA-(58x)-AAAA AABBB-(38x)-BBBBB
.....
(n-1)th: BBBBB-(39x)-BBBBA AAAAA-(59x)-AAAB
nth: BBBBB-(40x)-BBBBB AAAAA-(60x)-AAAA
and perform the n calculations for the different structures.
Finally you may calculate the weighted sums to find some average
</pre>
</blockquote>
<pre wrap=""><!---->properties.
</pre>
<blockquote type="cite">
<pre wrap="">
Actually I don't think I would perform supercell calculations to find the
</pre>
</blockquote>
<pre wrap=""><!---->properties of random alloys,
</pre>
<blockquote type="cite">
<pre wrap="">just before someone complains.
Ciao
Gerhard
====================================
Dr. Gerhard H. Fecher
Institut of Inorganic and Analytical Chemistry
Johannes Gutenberg - University
55099 Mainz
________________________________________
Von: <a class="moz-txt-link-abbreviated" href="mailto:wien-bounces@zeus.theochem.tuwien.ac.at">wien-bounces@zeus.theochem.tuwien.ac.at</a>
</pre>
</blockquote>
<pre wrap=""><!---->[<a class="moz-txt-link-abbreviated" href="mailto:wien-bounces@zeus.theochem.tuwien.ac.at">wien-bounces@zeus.theochem.tuwien.ac.at</a>] im Auftrag von Ghosh SUDDHASATTWA
[<a class="moz-txt-link-abbreviated" href="mailto:ssghosh@igcar.gov.in">ssghosh@igcar.gov.in</a>]
</pre>
<blockquote type="cite">
<pre wrap="">Gesendet: Dienstag, 29. Dezember 2009 14:31
An: 'A Mailing list for WIEN2k users'
Betreff: Re: [Wien] [Wien2k Users] Structure Generation of Solid Solution
</pre>
</blockquote>
<pre wrap=""><!---->inWien2k
</pre>
<blockquote type="cite">
<pre wrap="">Dear Dr. Lawrence,
Thanks for the reply,
I have AB solid solution with A and B both occupying 10 different
nonequivalent positions.
That is to say we have a total of 10 different positions for A as well as
for B.
The atomic positions are all same.
With this, when I try to save the structure, it gives the error as same
</pre>
</blockquote>
<pre wrap=""><!---->atom
</pre>
<blockquote type="cite">
<pre wrap="">cannot occupy the same atomic position.
So the struct file is not generated at all.
So how do we run supercell in this condition.
Can a solution to this be given please.
Moreover, how do we specify 60 % of the sites to be occupied by A in the
supercell program.
Thanks
Suddhasattwa Ghosh
-----Original Message-----
From: <a class="moz-txt-link-abbreviated" href="mailto:wien-bounces@zeus.theochem.tuwien.ac.at">wien-bounces@zeus.theochem.tuwien.ac.at</a>
[<a class="moz-txt-link-freetext" href="mailto:wien-bounces@zeus.theochem.tuwien.ac.at">mailto:wien-bounces@zeus.theochem.tuwien.ac.at</a>] On Behalf Of Laurence
</pre>
</blockquote>
<pre wrap=""><!---->Marks
</pre>
<blockquote type="cite">
<pre wrap="">Sent: Tuesday, December 22, 2009 2:25 PM
To: A Mailing list for WIEN2k users
Subject: Re: [Wien] [Wien2k Users] Structure Generation of Solid Solution
inWien2k
To make a solid solution like this you need to generate a supercell
and occupy 60% of the sites with "A", and 40% of the sites with "B".
The supercell needs to be "large enough" for this to represent an
effective random distribution, and you can probably find some
literature on how large this needs to be (or maybe someone can give
relevant references).
On Mon, Dec 21, 2009 at 11:00 PM, Ghosh SUDDHASATTWA
<a class="moz-txt-link-rfc2396E" href="mailto:ssghosh@igcar.gov.in"><ssghosh@igcar.gov.in></a> wrote:
</pre>
<blockquote type="cite">
<pre wrap="">Dear Wien2k users
[SuddhasattwaGhosh]
In case the crystal structure of solid solution A0.6B0.4 is available,
</pre>
</blockquote>
<pre wrap="">where
</pre>
<blockquote type="cite">
<pre wrap="">A and B both occupy equivalent positions, is it possible to generate the
structure using StructGen in Wien2k.
How can mixed character of lattice points be handled in Wien2k?
Suddhasattwa Ghosh
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</pre>
</blockquote>
<pre wrap="">
--
Laurence Marks
Department of Materials Science and Engineering
MSE Rm 2036 Cook Hall
2220 N Campus Drive
Northwestern University
Evanston, IL 60208, USA
Tel: (847) 491-3996 Fax: (847) 491-7820
email: L-marks at northwestern dot edu
Web: <a class="moz-txt-link-abbreviated" href="http://www.numis.northwestern.edu">www.numis.northwestern.edu</a>
Chair, Commission on Electron Crystallography of IUCR
<a class="moz-txt-link-abbreviated" href="http://www.numis.northwestern.edu/">www.numis.northwestern.edu/</a>
Electron crystallography is the branch of science that uses electron
scattering and imaging to study the structure of matter.
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</pre>
</blockquote>
<pre wrap=""><!---->
--
-----------------------------------------
Peter Blaha
Inst. Materials Chemistry, TU Vienna
Getreidemarkt 9, A-1060 Vienna, Austria
Tel: +43-1-5880115671
Fax: +43-1-5880115698
email: <a class="moz-txt-link-abbreviated" href="mailto:pblaha@theochem.tuwien.ac.at">pblaha@theochem.tuwien.ac.at</a>
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</blockquote>
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