[Pw_forum] Help in cif file atomic positions

Fri Oct 7 16:04:18 CEST 2016

I guess an easy yet efficient way for generating your alloy structure is to
use the Monte Carlo SQS (mcsqs) module which is part of the ATAT gnu
software available from:
https://www.brown.edu/Departments/Engineering/Labs/avdw/atat/

M A H Khalafalla
Taibah University
Dept of Physics

On Friday, October 7, 2016, Krishnaiah Kallamadi <krishnsustain at gmail.com>
wrote:

> Dear Sir,
>
> Thanks a lot
>
> On Fri, Oct 7, 2016 at 7:05 PM, Michael Mehl <mmehl at usna.edu
> <javascript:_e(%7B%7D,'cvml','mmehl at usna.edu');>> wrote:
>
>> [image: Boxbe] <https://www.boxbe.com/overview> This message is eligible
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>>
>> Since C and N are neighbors in the periodic table, you could put a
>> "virtual" atom at the site, with charge Z = 6.5.  That would at least give
>> you the right electron count for the system and preserve the system
>> symmetry.  The downside is that a pseudopotential for "Cargen" or
>> "Nitrobon" probably doesn't exist, so you'd have to generate it yourself.
>> I think VASP is able to handle this somehow, but I've never tried it.
>>
>> Another alternative is to generate a supercell, randomly populate that
>> site with C and N atoms, and average over configurations.  Look up various
>> articles by Alex Zunger et al. (http://journals.aps.org/prl/a
>> bstract/10.1103/PhysRevLett.65.353, to start) on Special Quasirandom
>> Structures for some hints on how to do this efficiently.  The downside of
>> this is that you'll need a fair number of structures, and you'll lose the
>> hexagonal symmetry in the individual calculations.
>>
>> AFAIK, there aren't any really good solutions for this problem with the
>> current generation of DFT codes.  At one time there was some work with the
>> Coherent Potential Approximation and KKR (see http://journals.aps.org/p
>> rb/pdf/10.1103/PhysRevB.67.115109, e.g.), but I don't think any modern
>> KKR codes are easily available, much less KKR+CPA.
>>
>> On Fri, Oct 7, 2016 at 7:50 AM, Krishnaiah Kallamadi <
>> krishnsustain at gmail.com
>> <javascript:_e(%7B%7D,'cvml','krishnsustain at gmail.com');>> wrote:
>>
>>> As per my knowledge,
>>> espresso can't deal with above cif file. Please help me and correct if I
>>> am wrong.
>>>
>>> On Fri, Oct 7, 2016 at 11:33 AM, Andrius Merkys <
>>> andrius.merkys at gmail.com
>>> <javascript:_e(%7B%7D,'cvml','andrius.merkys at gmail.com');>> wrote:
>>>
>>>> [image: Boxbe] <https://www.boxbe.com/overview> This message is
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>>>>
>>>> Dear Krishna,
>>>>
>>>> On 07/10/16 08:30, Krishnaiah Kallamadi wrote:
>>>>
>>>> In a *cif* file attached below, two different atoms have same atomic
>>>> positions with occupancy of 0.5. Due to this i am not able to generate *scf.in
>>>> <http://scf.in>* file from cif2cell program. Please help me.
>>>>
>>>>
>>>> you have to account for a joint 0.5N+0.5C site at this position. I am
>>>> not sure if/how such thing is possible at QE input, but AFAIK, people are
>>>> dealing with such models.
>>>>
>>>> HTH,
>>>> Andrius
>>>>
>>>> --
>>>> Andrius Merkys
>>>> PhD student at Vilnius University Institute of Biotechnology, SaulÄ—tekio al. 7
>>>> LT-10223 Vilnius, Lithuania
>>>>
>>>>
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>>>>
>>>
>>>
>>> --
>>> Thanks and Regards,
>>>
>>> K.Krishna
>>> JRF, AcSIR-RE
>>> CSIR-SERC
>>>
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>>
>>
>>
>> --
>>
>> [image: USNA_Gold_Seal.png]
>>
>> Michael J. Mehl, Ph.D.
>>
>> Kinnear Chair in Physics
>>
>> The United States Naval Academy
>>
>> Mail Stop 9C
>>
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>>
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>>
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>>
>>
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>
>
> --
> Thanks and Regards,
>
> K.Krishna
> JRF, AcSIR-RE
> CSIR-SERC
>

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