[Wien] setup of slab calculation

[Torsten Andersen]

Dear Fred,

Fred Nastos wrote:
> Hi,
> 
> I am certain these have been asked before, but I looked through the archives 
> and could not find the answer.
> 
> Q1) The .struct file has to have the coordinates specified as positive ratios 
> of the unit cell parameters, i.e. they are relative to the unit cell 
> parameters.  If I am doing the slab calculation, and I want to increase the 
> amount of vacuum, that makes one of my cell parameters larger.  Does that 
> mean I need to change the relative coordinates of the atoms by hand?  I could 
> write something to do this, but is there some utility that does that 
> allready?  Or, am I totally out to lunch on this?

This is correct. I don't know of any existing programs for that. I do it 
by hand, since it only has to be done once for each slab. Anyway, since 
I made a little csh-script to check for distances in optimized slabs vs. 
the bulk lattice, I am sure you can make a similar script to change 
these values (sed, bc, awk, tail and head should do it, I think).

> 
> Q2) I made a struct file for a supercell without specifying any symmetry 
> matrices.  When I tried to initialize my calculation, the sgroup program 
> changed my choice of axis, and gave me a new struct file.  My "growth axis", 
> which was originally in the z-direction, was changed to be along the 
> x-direction.
> 
> I know that accepting the changes works fine [1], and I can live with the 
> changes, but is it possible to neglect the warnings and run the code with my 
> original choice of axes?  I would guess that I just need to be careful about 
> the symmetry matrices I provide at the end of the struct file, no?

This should be possible. And "symmetry" will find the right symmetries 
for you without chaning the lattice or axes. In this case you can ignore 
"sgroup".

> 
> Thank you for your time.

No problem.

> 
> [1] I verified that the WIEN code results from the modified structure file 
> (the band structure, the linear optics, etc..) were comparable to those from 
> a pseudopotential code which doesn't change the axes choice.
> 
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Best regards,
Torsten Andersen.

-- 
Dr. Torsten Andersen        TA-web: http://deep.at/myspace/
AG Hübner, Department of Physics, Kaiserslautern University
http://cmt.physik.uni-kl.de    http://www.physik.uni-kl.de/