[Wien] [Wien2k Users] Structure Generation of Solid Solution in Wien2k
Rocquefelte
Xavier.Rocquefelte at cnrs-imn.fr
Sat Jan 9 14:43:15 CET 2010
I looked to all the mails concerning your question and I would like to
clarify some points:
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):
- the size of the cell (translational symetry)
- the space group (equivalent positions...).
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).
If you properly generate such a supercell and impose P1 symetry then you
will have no more problems.
In my case, I usually generate such a supercell using the following
strategy:
- consideration of the experimental structure (small cell / high
symetry) in a visualization program such as Endeavour or Diamond
- remove any partial occupancies
- transformation of the structure into P1 (this could be easily done
with Endeavour or by hand)
- generation of a supercell using an internal program or excel or any
program allowing to recalculate the new fractional coordinates
- occupation of the previously equivalent sites (for translation or
space group symetry reasons) by A and B
- save the so-obtained file in cif format
- use the program cif2struct to generate a proper struct file
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 ...).
Best Regards
Xavier
Ghosh SUDDHASATTWA a écrit :
> 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: wien-bounces at zeus.theochem.tuwien.ac.at
> [mailto:wien-bounces at zeus.theochem.tuwien.ac.at] 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: wien-bounces at zeus.theochem.tuwien.ac.at
> [wien-bounces at zeus.theochem.tuwien.ac.at] im Auftrag von Peter Blaha
> [pblaha at theochem.tuwien.ac.at]
> 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:
>
>> First a question, how is the bandstructure defined in a random alloy when
>>
> the infinite periodicity is lost ?
>
>> To specify 60 % of the sites to be occupied by A, you need a supercell say
>>
> with 100 atoms and
>
>> to set 60 of the sites by A and 40 by B atoms (always one atom no fraction
>>
> !)
>
>> this you have to do for all distinguishable (!) permutations (use some
>>
> statistics !)
>
>> 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
>>
> properties.
>
>> Actually I don't think I would perform supercell calculations to find the
>>
> properties of random alloys,
>
>> just before someone complains.
>>
>> Ciao
>> Gerhard
>>
>> ====================================
>> Dr. Gerhard H. Fecher
>> Institut of Inorganic and Analytical Chemistry
>> Johannes Gutenberg - University
>> 55099 Mainz
>> ________________________________________
>> Von: wien-bounces at zeus.theochem.tuwien.ac.at
>>
> [wien-bounces at zeus.theochem.tuwien.ac.at] im Auftrag von Ghosh SUDDHASATTWA
> [ssghosh at igcar.gov.in]
>
>> Gesendet: Dienstag, 29. Dezember 2009 14:31
>> An: 'A Mailing list for WIEN2k users'
>> Betreff: Re: [Wien] [Wien2k Users] Structure Generation of Solid Solution
>>
> inWien2k
>
>> 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
>>
> atom
>
>> 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: wien-bounces at zeus.theochem.tuwien.ac.at
>> [mailto:wien-bounces at zeus.theochem.tuwien.ac.at] On Behalf Of Laurence
>>
> Marks
>
>> 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
>> <ssghosh at igcar.gov.in> wrote:
>>
>>> Dear Wien2k users
>>> [SuddhasattwaGhosh]
>>>
>>> In case the crystal structure of solid solution A0.6B0.4 is available,
>>>
>> where
>>
>>> 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
>>>
>>>
>>>
>>> _______________________________________________
>>> Wien mailing list
>>> Wien at zeus.theochem.tuwien.ac.at
>>> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>>>
>>>
>>
>> --
>> 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: www.numis.northwestern.edu
>> Chair, Commission on Electron Crystallography of IUCR
>> www.numis.northwestern.edu/
>> Electron crystallography is the branch of science that uses electron
>> scattering and imaging to study the structure of matter.
>> _______________________________________________
>> Wien mailing list
>> Wien at zeus.theochem.tuwien.ac.at
>> http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
>>
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>
> --
> -----------------------------------------
> Peter Blaha
> Inst. Materials Chemistry, TU Vienna
> Getreidemarkt 9, A-1060 Vienna, Austria
> Tel: +43-1-5880115671
> Fax: +43-1-5880115698
> email: pblaha at theochem.tuwien.ac.at
> -----------------------------------------
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