[Pw_forum] [pw_forum] how to set up spin-orbital coupling calculation in PWscf

[Stefano Baroni]

Zhiping:

I wish Andrea's reply fully clarifies the practical side of the  
problem. I would like to make sure, though, that my previous note  
(saying that in the presence of SO interactions electronic states are  
always psin polarized) is properly understood. Here is a summary of  
how SO coupling was explained to me long, LONG, ago.

In the reference frame of any electron the electron is - by  
definition - at rest, but the other charges (including nuclei - or  
screened nuclei, i.e. frozen ions) are not. The other charges are  
therefore associated to currents that generate a magnetic field  
which, in turns, interacts with the spin at rest, determining an  
alignement of the electron spin along its direction. Hence, the  
electron is polarized. The magnitude and direction of the magnetic  
field depends on the position of the electron, and so the resulting  
spin polarization will depend on position. In order to describe a  
spin polarization that depends on position, you will need to describe  
electron states with two-component spinors. This is what the  
"noncolin=.true." keyword is sipposed to mean ("non colin" for "non  
collinear (spin) polarization).

Hope this clarifies a bit more.

Also, remember: computer codes (Wien2k, pwscf, you name it) are fun,  
but the reason why they work and the way they work is even more fun!

Have fun with electronic structure calculations!

Stefano

On Jul 27, 2007, at 8:58 AM, Dal Corso Andrea wrote:

> On Thu, 2007-07-26 at 15:50 -0700, Zhiping Yin wrote:
>> Dear PWscf users,
>>
>> I tried to set up spin-orbital coupling calculation in PWscf without
>> spin polarization. I used a full relativistic NCPP and set
>> lspinorb=.true.. However, the output is identical with
>> lspinorb=.false. I wonder what is the correct way to set up a
>> spin-orbital coupling calculation with/without spin polarization.  
>> What
>> is the requirement with the pseudopotential. Thanks very much.
>>
>
> The following input variables are relevant for a spin-orbit  
> calculation:
>
> noncolin=.true.
> lspinorb=.true.
>
> starting_magnetization
>
> To make a spin-orbit calculation noncolin must be true. If it is false
> lspinorb is set to false no matter what you give as input.
>
> If starting_magnetization is set to zero (or not given)  the code  
> makes
> a spin orbit calculation without spin magnetization (it assumes that
> time reversal is true and it does not calculate the magnetization).
> The states are still two component spinors but the total magnetization
> is zero.
>
> If starting_magnetization is different from zero it makes a non
> collinear spin polarized calculation with spin orbit. The final spin
> magnetization might be zero or different from zero depending on the
> system.
>
> Furthermore to make a spin-orbit calculation you must use fully
> relativistic pseudopotentials at least for the atoms in which you  
> think
> that spin orbit is large. If all the pseudopotentials are scalar
> relativistic the calculation becomes equivalent to a noncolinear
> calculation without spin orbit.
>
> Hope this helps,
>
> Andrea
>
>> Best,
>> Zhiping Yin
>>
>> -- 
>> Zhiping Yin
>> graduate student
>> department of physics
>> UC Davis
>> _______________________________________________
>> Pw_forum mailing list
>> Pw_forum at pwscf.org
>> http://www.democritos.it/mailman/listinfo/pw_forum
> -- 
> Andrea Dal Corso                    Tel. 0039-040-3787428
> SISSA, Via Beirut 2/4               Fax. 0039-040-3787528
> 34014 Trieste (Italy)               e-mail: dalcorso at sissa.it
>
>
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---
Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center -  
Trieste
[+39] 040 3787 406 (tel) -528 (fax) / stefanobaroni (skype)

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