[Wien] AFM calculations- surface calculation

[Peter Blaha]

> SUMMARY
> 
>   2. I am confusing  on preparing proper structure file. : AFM, 
> Non-magnetic(NM) file .
>       Space group selection after the 'x sgroup' : Am I have to say 
> 'yes' for the NM calc. ?? or 'No' for the AFM ?

I cannot give a definite answer. WIEN2k has 2 programs (nn and sgroup)
which can check your input structure.
nn will analyze distances and when it finds that two atoms have equal
neighborhood, it will create a new struct file for you and make these
two atoms equivalent. However, nn works with the names of the atoms
only, i.e. it does not know when you want to make ONE atom spin-up and
the other one spin-dn. You can tell the program that two C atoms should
be "different" even when they have the same environment by specification
of a number after the element namelike "C 1" and "C 2".

When you do this, you probably should follow the suggestions of nn until
it does not complain anymore.

The sgroup program can do even "more", namely reduce the unit cell,
change translation vectors,.... However, sometimes there are several
possibilities to setup a structure and sgroup may NOT use the setup you
like (eg. because you want to compare nm and afm structures and thus
want to keep same orientations,... In such a case you can neglect sgroup.
But if you e.g. constructed a too large unit cell, you cannot neglect
this, unless you make some more atoms non-equivalent.

There is a third program, symmetry, which will crosscheck your decisions
and if you do not find any error (warning) in case.outputs, it should be
fine.

>   3. I cannot state spin cofiguration for the AFM-up or AFM-dn and 
> NM-zero atoms in the 'case_AFM.inst' file.

Read my answers 2 days ago to a similar question. Switch to the latest
release.

>   4. What dose It mean TRANSLATION VECTOR which transforms the spin-up 
> into the spin-dn atom. The prepared example of the Cr case is make sense 
> to me, however
>       how can I make it with my surface danglin bonds.

My suggestion: forget about  running x afminput and runafm_lapw (which
requires the definition of symmetry operations between the AFM atoms),
but just use runsp_lapw (its 2 times more expensive, but more "save").
In this case, just stop after "spin-polarization" (but still you need to
set the proper AFM spin-configuration in case.inst).
-- 
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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
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