[Wien] change of lattice parameters while alloying

[Víctor Luaña Cabal]

On Tue, May 09, 2017 at 10:15:22PM +0530, Dr. K. C. Bhamu wrote:
> Thank you Prof. Peter for detailed reply,
> May be I still have some doubts on symmetries and need to read some
> literature.
> For meanwhile, from literature I came to know that the distortion in my
> doped structure "change in unit cell ("lattice parameters and angles")"
>  may occur depending on size effects, deviations from the ideal composition
> and the JTE etc.
> 
> So what I am doing is good and there is no way to preserve the same SG/unit
> cell.
> 
> I  tried to maintain the original structure and got below warnings which
> support my above understanding:
> 

Dr. Bhamu,

It is a cultural division, but crystalographers have a better
perspective, in my opinion, than solid state physicists on the
description of solids. Traditionally solid state teory has been very
much related to the treatement of simple structures and only recently
complex crystals have been affordable to quantum treatment.

You have an excellent test: "Fundamentals of crystallography" by C.
Giacovazzo et al.
"Chapter 1: symmetry of crystals" is a must reading if you want to master
the subject.

wien2k interface started from the perspective of treating simple solids,
but a crystallographicaly adapted code could be able to deal with
something like

crystal
   spacegroup  F m -3 m
   cell  a
   atom Cr 0 0 0
   atom B  0.5 0.5 0.5
   optimize a
end

So you should take account of: (a) the space group; (b) the celll parameters
compatible with the space group; (c) the Wyckoff positions occupied in
your structure. The Bilbao crystallographic server has a lot of tools:

<http://www.cryst.ehu.es/#retrievaltop>

In this case the WYCKPOS tool provides the starting information.

Alberto Otero-de-la-Roza developed some time ago a runwien interface for
wien2k that was able to do a restricted version of this approach. It was
part of his PhD thesis, in fact. One in 8 or 9 chapters. That interface
was published as

@article{OterodelaRoza2009RunwienAT,
  title={Runwien: a text-based interface for the WIEN package},
  author={A. Otero-de-la-Roza and V{\'i}ctor Lua{\~n}a},
  journal={Computer Physics Communications},
  year={2009},
  volume={180},
  pages={800-812}
}

The source can be found in

<https://github.com/aoterodelaroza/runwien>

but some adaptation *may* be needed for the current wien2k.

Best regards,
              Dr. Víctor Luaña
--
    .  .    "De la cuna a la tumba es una escuela, por eso lo que llamas 
   / `' \   problemas son lecciones."
  /(o)(o)\  -- Facundo Cabral, Cuna
 /`. \/ .'\ 
/   '`'`   \
|  \'`'`/  | 
|  |'`'`|  | 
 \/`'`'`'\/  
==(((==)))===================================+===========================
! Dr.Víctor Luaña, in silico chemist & prof. !
! Departamento de Química Física y Analítica !
! Universidad de Oviedo, 33006-Oviedo, Spain !
! e-mail:  <victor at fluor.quimica.uniovi.es>  !
! phone: +34-985-103491  fax: +34-985-103125 !
+--------------------------------------------+
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