[Wien] Slab symmetry with SOC

pluto at physics.ucdavis.edu pluto at physics.ucdavis.edu
Sat Dec 14 14:48:44 CET 2013 

Dear Prof. Blaha, dear Gerhardt,

Prof. Blaha, thank you for this detailed procedure :-)

I tried this today. What happens, is that nn and sgroup create *.struct
file with space group 123, and 8 unique atoms (15 atoms total). The atoms
on the opposite sides of the slab are merged into a single unique
position.

Calculation with SOC needs to have the atoms on the opposite sides of the
slab splitted. However, initso_lapw does not split anything, and the
*.struct (and *.struct_so) file stays pretty much the same as before, at
least it again has only 8 unique atoms (15 total). As a result, after
running SCF with SOC and sp I will not be able to separate the surface
electronic structures on the opposite sites of the slab (along the
in-plane axis orthogonal to the magnetization they will differ).

Is it allowed/possible to use a primitive cell, and manually include the
2-fold rotation axis (which would be identical to the magnetization axis)?

Regards,
Lukasz



On 12/13/2013 8:38 PM, Peter Blaha wrote:
> 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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-- 
Dr. Lukasz Plucinski

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