[Wien] Calculation spin-orbit coupling with two different approach gives different results

[Laurence Marks]

Let me add one small thing to what Peter said. Be careful to check that you
truly have a converged density. It is possible for the scf iterations to
converge to a trap where the density (:DIS etc) is converged but the
orbital terms (:MVORD) are not self-consistent. I would estimate that for a
self-consistent orbital potential :MVORD should be less than 1%. It can be
necessary to take some measures to climb out of local traps like this, for
instance by doing "echo 0.1 > .pratt" to force a Pratt step to be included.
This can be important when -so is included, and in a few cases when it is
not.

On Mon, Nov 23, 2015 at 7:45 AM, Santu Baidya <santubaidya2009 at gmail.com>
wrote:

> Dear Prof. Blaha,
>
>   Thank you very much for you reply on this. Actually I did relax the
> structure under GGA+U approximation. Then took two approaches.  In one case
> I did SCF calculation under GGA+U with relaxed structure  and added SOC
> afterthat. In other case I took relaxed structure and did GGA+U+SOC
> calculation.
> Which gave me two different electronic structure for the same relaxed
> structure.
>
> So I have to take lowest energy structure.
>
> Thanking you and regards,
>
> Santu Baidya
>
>
>
>
>
> On 23 November 2015 at 18:58, Peter Blaha <pblaha at theochem.tuwien.ac.at>
> wrote:
>
>> It is well know that GGA+U calculations can end up in different states
>> (see previous posts).
>>
>> If you have used the same parameters, you should use the total energies
>> of the two calculations and the one with lower energy should be the better
>> one (but not necessarily the best !)
>>
>> In any case, I always recommend:
>>
>> First do a standard GGA calculation (also check forces, if they are
>> small).
>> Then add SO and do a GGA+SO calculation (if you really have heavy
>> elements?)
>> x lapwdm -up -so      to generate density matrices
>>
>> and finally add the "U" and do   GGA+so+U
>>
>> There is, however, no guarantee that you find the lowest energy ground
>> state !  Sometimes it is good to start with a smaller U-value than
>> anticipated.
>> Sometimes you may do a structure relaxation at the GGA-level and use this
>> structure,
>> or a structure relaxation at GGA+U (no SO).
>>
>> If SO is not a major effect, I'd first do everything without SO.
>>
>> -------------------
>> From these advices you can see that there is not a unique and save way,
>> which works in all cases.
>>
>>
>>
>> On 11/23/2015 12:10 PM, Santu Baidya wrote:
>>
>>> Dear Prof. Blaha and wien2k users,
>>>
>>>       I use wien2k version WIEN2k_14.1. Recently I did spin-orbit
>>> coupling calculation under GGA+U+SOC approximation with two different
>>> approaches- one starting from collinear ground state and another
>>> starting from scratch (random wavefunction). Two approaches give me
>>> completely different results -metal and insulator.
>>>
>>> Please tell me which approach should I accept as solution.
>>>
>>> I look forward to get reply.
>>>
>>> Thanking you,
>>>
>>> Santu Baidya
>>> University of Duisburg-Essen
>>> Duisburg
>>>
>>>
>>>
>>>
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>>>
>> --
>>
>>                                       P.Blaha
>> --------------------------------------------------------------------------
>> Peter BLAHA, Inst.f. Materials Chemistry, TU Vienna, A-1060 Vienna
>> Phone: +43-1-58801-165300             FAX: +43-1-58801-165982
>> Email: blaha at theochem.tuwien.ac.at    WIEN2k: http://www.wien2k.at
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>> --------------------------------------------------------------------------
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>
>


-- 
Professor Laurence Marks
Department of Materials Science and Engineering
Northwestern University
www.numis.northwestern.edu
Corrosion in 4D: MURI4D.numis.northwestern.edu
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
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