[Wien] [Wien2k Users] Structure Generation of Solid Solution inWien2k

[Peter Blaha]

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