[Wien] setup of slab calculation

[Fred Nastos]

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?

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?

Thank you for your time.

[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.