[Wien] Slab symmetry with SOC

Peter Blaha pblaha at theochem.tuwien.ac.at
Fri Dec 13 20:38:04 CET 2013


Lets start "systematic". There's nothing simpler than creating
a (001) surface:

Forget spin-orbit at the moment, just create a slab.

Take a unit cell of bcc-Fe   and

x supercell   with 1x1x7, add vacuum in z (eg. 30 bohr, your 15 bohr are a little too small)
               and "repeat atom at z=0".

Take the resulting struct file and run "several times"
x nn   (always accept the created struct file).
x sgroup   (sgroup will shift for you the positions, so that
             you have a symmetric slab with inversion symmetry.
             accept the struct file from sgroup).

You can now do:

init_lapw -b -sp -numk 400 (maybe with fermit 0.004, because we have
                             a 2D BZ and TETRA may have problems).
runsp -fc 1    converge and optimize positions (MSR1a).

save_lapw

Now you can run    initso_lapw
   Define magnetization direction and say "spin-polarization" yes.
   This runs symmetso and depending on the direction of M it may/may not
   reduce symmetry. Accept the structure and run

runsp -I -so


Am 13.12.2013 18:28, schrieb pluto at physics.ucdavis.edu:
> Dear Gerhard,
>
> Thank you for your comment.
>
> I have a feeling, that my system has an inversion symmetry from the point
> of view of the electronic structure. If you think of surface electronic
> structure and surface Brillouin zone, then the surface electronic
> structures on both sides of the slab must be the same, only inverted with
> respect to surface-Gamma. The inversion is there, because in my particular
> case electronic structure is the same along the magnetization-axis and
> along minus-magnetization-axis.
>
> In any case (with or without inversion symmetry) the 180deg rotation
> around the magnetization axis is one of the symmetry operations of my
> slab. How can I include it in my calculation using the w2web interface?
>
> Regards,
> Lukasz
>
>
>
> SO has no inversion symmetry
> Think about the spin when you apply an inversion.
>
> Ciao
> Gerhard
>
> DEEP THOUGHT in D. Adams; Hitchhikers Guide to the Galaxy:
> "I think the problem, to be quite honest with you,
> is that you have never actually known what the question is."
>
> ====================================
> Dr. Gerhard H. Fecher
> Institut of Inorganic and Analytical Chemistry
> Johannes Gutenberg - University
> 55099 Mainz
> ________________________________________
> Von: wien-bounces at zeus.theochem.tuwien.ac.at
> [wien-bounces at zeus.theochem.tuwien.ac.at]" im Auftrag von
> "pluto at physics.ucdavis.edu [pluto at physics.ucdavis.edu]
> Gesendet: Freitag, 13. Dezember 2013 18:02
> An: wien at zeus.theochem.tuwien.ac.at
> Betreff: Re: [Wien] Slab symmetry with SOC
>
> Dear Prof. Blaha, dear Wien2k users,
>
> I attach the most symmetric slab which I was able to produce. I try with
> 15 atoms in order to save time with testing, later I am planning to do a
> larger slab. You could see that now the surface normal is <100>, I started
> with <001>, but sgroup swapped axes -- but this is fine. So now the
> in-plane magnetization is along <001>, and it's the same as the mirror
> plane normal axis (becuase the space group is the 6_Pm with the unique
> c-axis).
>
> I believe that my system should have an inversion symmetry even with SOC.
> And at the same time I believe that the two surface atoms (in this case
> atom 1 and atom 15) should have their unique positions (they should not be
> merged into a single position as they would without SOC).
>
> I would appreciate the advice on how to make a spin-polarized calculation
> with SOC on this slab with included inversion symmetry. So far I have a
> mirror plane, so it would also be ok to only add a 2-fold 180deg rotation
> around the magnetization axis.
>
> Regards,
> Lukasz
>
>
>
>
>
> On 12/13/2013 11:22 AM, Peter Blaha wrote:
>> For a spin-polarized case you should use init_so and the program
> symmetso.  Symmetso should give you the proper symmetries and one should
> use the struct file produced by symmetso. There should be a
> classification of each of the symmetry operations of the non-so case
> according to A, B or none.
>>
>> I can hardly comment on a specific feature without doing the slab myself.
>>
>> Please have a look into the lecture notes about spin-orbit coupling and
> the reduction of symmetry due to so (from our web-site). There is a plot
> and table for a small specific example.
>>
>> Hwoever, note two remarks:   sgroup is completely irrelevant for this
> (as it does not know about spin-orbit).
>>
>> symmetso is obviously not as much tested as sgroup or symmetry. So be
> sure to use the latest version.
>> If you have doubts about symmetso, I need the struct file and the
> specific concerns.
>>
>> On 12/13/2013 10:00 AM, pluto at physics.ucdavis.edu wrote:
>>> Dear WIEN2k experts,
>>>
>>> Unfortunately nobody has commented on my email below.
>>>
>>> I believe that in my 15-atom Fe(001) slab, with magnetization along 100
>>> and SOC included, there will be a mirror 100 plane (space group 6).
>>> However, I have a feeling that there are more symmetries. For example I
>>> have a feeling, that there should be an inversion symmetry, or at least
>>> that the 100 axis should be a two-fold rotation axis. I am not able to
>>> include these symmetries.
>>>
>>> My calculations work well with fully primitive cell, and also with space
>>> group 6 (actually sgroup rotates the slab, so that mirror plane becomes
>>> 001, but this of course does not matter). But I think that in every
>>> problem one should include the necessary symmetries a priori, not only to
>>> save time, but to avoid some spurious results.
>>>
>>> Could you please give me at least some hint? I could also send my slab if
>>> necessary.
>>>
>>> Regards,
>>> Lukasz
>>>
>>>
>>>
>>>
>>>
>>> On 12/5/2013 10:03 AM, pluto at physics.ucdavis.edu wrote:
>>>
>>> Dear WIEN2k experts,
>>>
>>> I am calculating 29-atom Fe(001) slab with SOC with easy axis along [100].
>>>
>>> Without SOC one can find more symmetries, and one has only 15 inequivalent
>>> atoms. However, when performing the calculation with such slab the results
>>> are different compared to the complex calculation with "pure" slab of 29
>>> atoms. I believe that the correct result in this calculation is that
>>> surface bands along [100] and [-100] are the same, and bands along [010]
>>> and [0-10] are different. So one should have 3 slightly different set of
>>> surface bands: along [100] (identical to [-100]), [010], and [0-10].
>>>
>>> Of course on the opposite surfaces of the slab things will have the
>>> inversion symmetry.
>>>
>>> I believe that one of the programs, e.g. symmetso should in principle be
>>> able to find out, whether the symmetries are correct or not, and produce
>>> the correct struct file, which is possibly a bit more symmetric than the
>>> original file.
>>>
>>> Please advise.
>>>
>>> Regards,
>>> Lukasz
>>>
>>>
>>>
>>>
>>>
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>
>
> --
> Dr. Lukasz Plucinski
> _______________________________________________
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>
>
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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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