[Wien] A few (more) elementary -so questions (with onsite -eece)

pieper pieper at ifp.tuwien.ac.at
Wed May 6 14:30:28 CEST 2015 

Sorry, the comment was confusing.

The spin moments specified in the initial configuration of course point 
along the axis specified by the direction.

What I wanted to point out is that for symmetry reasons this is the only 
meaningfull component you can specify. In this sense symmetry comes 
first. The direction is more than just the spin direction. Its the only 
direction along which any vector operator that Wien2k can represent in 
the given case can point.

Someone should correct me if I am wrong, but in my understanding this is 
(one of) the reason(s) that Wien2k can only cope with collinear magnetic 
moments: The axial symmetry is introduced as a global symmetry. The 
direction of the axis is the same in all muffin-tin spheres. I expect 
the Wienncm code handles this on basis of the local symmetry.


---
Dr. Martin Pieper
Karl-Franzens University
Institute of Physics
Universitätsplatz 5
A-8010 Graz
Austria
Tel.: +43-(0)316-380-8564


Am 05.05.2015 19:31, schrieb Laurence Marks:
> I would be interested in clarification from others, but from what I
> can see in the code it appears that this is the spin direction that is
> used, not just the direction of breaking the symmetry. I may be wrong.
> 
> On Tue, May 5, 2015 at 11:47 AM, pieper <pieper at ifp.tuwien.ac.at>
> wrote:
> 
>> I definitely am not an expert for -so, therefore I will not shoot
>> down
>> anything, only a comment:
>> 
>>  From my point of view from magnetism I would ask for some caution
>> with
>> identifying the direction given in .inorb and .inso with 'the spin
>> direction'. As Gerhard pointed out earlier in this thread, it's all
>> about symmetry: The specified direction only sets up the symmetry
>> of the
>> case to be compatibel with whatever has a rotational invariance
>> with
>> that (quantization) axis - be that a spin, or orbital moment,
>> magnetization, a magnetic field, ... The symmetry of the basis has
>> to
>> allow for a magnetization otherwise it won't appear when you
>> calculate
>> expectation values. Personally I find Pavel's 'lecture on
>> spin-orbit.ps [1]'
>> here in the Wien documentation files (I hope it's still there) very
>> illuminating.
>> 
>> ---
>> Dr. Martin Pieper
>> Karl-Franzens University
>> Institute of Physics
>> Universitätsplatz 5
>> A-8010 Graz
>> Austria
>> Tel.: +43-(0)316-380-8564
>> 
>> Am 05.05.2015 14:51, schrieb Laurence Marks:
>>> Me a culpa, I should have checked the mailing list first for the
>>> answers.
>>> 
>>> That said, this issue has come up enough times in the past that I
>>> think the UG should be tweaked so it is clearer. Let me try my
>>> interpretation, so I can be shot down if needed.
>>> 
>>> Within Wien2k magnetic effects can be approximately included in a
>>> number of ways. Some such as the spin-orbit coupling assume a
>>> direction for the spin vector (for all electrons actively
>> considered),
>>> others such as Bext in orb specify a direction for an applied
>> magnetic
>>> field (in Tesla) and use the same direction for the spin vector.
>> (The
>>> two spin states are then either parallel or anti parallel to the
>>> specified direction.) When a direction is specified in case.inso
>> or
>>> case.inorb this fixes the spin vector and (if used) the external
>>> magnetic field direction. Via the output files from lapwdm
>>> (case.scfdmXX) one can monitor how the angular momentum changes
>> [1].
>>> By using different directions for the spin vector (and field) one
>> can
>>> probe how the energy changes and/orbital occupancies with assumed
>>> directions for the spin/external magnetic field.
>>> 
>>> To escape the assumption that the spin vectors all have one
>> direction
>>> the Wienncm code has to be used.
>>> 
>>> [1] My addendum. Changes in the occupancies can be a soft
>> electronic
>>> mode, i.e. very small changes in the energy for quite large
>> changes in
>>> the density. The older mixing algorithms (MSEC1 or MSEC3) are not
>> so
>>> good for soft modes and can stagnate. MSR1 is better and the next
>>> release (7.0) is much better. With onsite -eece &/or -orb it may
>> help
>>> to "push" the mixer by either forcing a larger step (echo .2 >
>> .msec
>>> or echo .1 > .pratt) or stopping, doing a force on the orbital
>>> potential (x orb -up; x orb -dn) then restarting with -NI. It is
>>> probably wise to check how the orbital momentum is converging
>> (grep
>>> :ORB0 *.scf, perhaps other) and make sure that the mixing is not
>>> starving (grep GREED: *.scf and check the values are not small,
>> e.g.
>>> 0.035).
>>> 
>>> ___________________________
>>>   Professor Laurence Marks
>>>   Department of Materials Science and Engineering
>>>   Northwestern University
>>>   www.numis.northwestern.edu [2] [1]
>>>   MURI4D.numis.northwestern.edu [3] [2]
>> 
>>>   Co-Editor, Acta Cryst A
>>>   "Research is to see what everybody else has seen, and to think
>> what
>>> nobody else has thought"
>>>   Albert Szent-Gyorgi
>>> On May 4, 2015 6:22 PM, "Laurence Marks"
>> <L-marks at northwestern.edu>
>>> wrote:
>>> 
>>>> Typo:
>>>> 
>>>> "although I remember don't symmetry operations being split into
>>>> these two classes everywhere in the code"
>>>> 
>>>> On Mon, May 4, 2015 at 6:04 PM, Laurence Marks
>>>> <L-marks at northwestern.edu> wrote:
>>>> 
>>>>> I am a newbie at -so, so a few simple questions.
>>>>> 
>>>>> a) What is the meaning of the orbital moment in case.scfdm* ?
>> Is
>>>>> that the average direction projected to the global axis system?
>>>>> 
>>>>> b) What is the physical significance of the orbital moment
>> being
>>>>> parallel (or not quite parallel) to the direction used in
>>>>> case.inso?
>>>>> 
>>>>> c) I understand that the results for different directions of B
>> in
>>>>> case.inso reflect the magnetic anisotropy, but what are the
>> units
>>>>> of field (if any)?
>>>>> 
>>>>> d) What else is worth looking at? The partial orbital moment
>>>>> (:POM) seems relevant, but what exactly is it?
>>>>> 
>>>>> e) I am "blindly" trusting that initso knows what it is doing,
>> and
>>>>> have left the "B" symmetry operations in case.struct (although
>> I
>>>>> remember symmetry operations being split into these two classes
>>>>> everywhere in the code). This seems to conflict with Pavel's
>>>>> notes, although those may be too old.
>>>>> 
>>>>> Thanks.
>>>>> 
>>>>> --
>>>>> 
>>>>> Professor Laurence Marks
>>>>> Department of Materials Science and Engineering
>>>>> Northwestern University
>>>>> www.numis.northwestern.edu [2] [1]
>>>>> Corrosion in 4D: MURI4D.numis.northwestern.edu [3] [2]
>>>>> Co-Editor, Acta Cryst A
>>>>> "Research is to see what everybody else has seen, and to think
>>>>> what nobody else has thought"
>>>>> Albert Szent-Gyorgi
>>>> 
>>>> --
>>>> 
>>>> Professor Laurence Marks
>>>> Department of Materials Science and Engineering
>>>> Northwestern University
>>>> www.numis.northwestern.edu [2] [1]
>>>> Corrosion in 4D: MURI4D.numis.northwestern.edu [3] [2]
>>>> Co-Editor, Acta Cryst A
>>>> "Research is to see what everybody else has seen, and to think
>> what
>>>> nobody else has thought"
>>>> Albert Szent-Gyorgi
>>> 
>>> 
>>> Links:
>>> ------
>>> [1] http://www.numis.northwestern.edu [2]
>>> [2] http://MURI4D.numis.northwestern.edu [3]
>> 
>>> 
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>>> 
>> 
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> 
> --
> 
> Professor Laurence Marks
> Department of Materials Science and Engineering
> Northwestern University
> www.numis.northwestern.edu [2]
> Corrosion in 4D: MURI4D.numis.northwestern.edu [3]
> Co-Editor, Acta Cryst A
> "Research is to see what everybody else has seen, and to think what
> nobody else has thought"
> Albert Szent-Gyorgi
> 
> Links:
> ------
> [1] http://spin-orbit.ps
> [2] http://www.numis.northwestern.edu
> [3] http://MURI4D.numis.northwestern.edu
> [4] http://zeus.theochem.tuwien.ac.at/mailman/listinfo/wien
> [5] 
> http://www.mail-archive.com/wien@zeus.theochem.tuwien.ac.at/index.html
> 
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