[Pw_forum] About NON COLLINEAR magnetism

[Stefano Baroni]

Dear Xianghjun:

the present version of PWscf cannot deal with spin spirals. An old 
version of it actually did. You may want to get in touch with Ralph 
Gebauer (rgebauer at ictp.trieste.it) for more details on the actual 
availability of that old version. Even better, you may want to 
volunteer and patch the routines for spirals contained in that old 
version into the new one ;-) Some details that you may find interesting 
(along with some nice ideas on magnon dynamics, constrained DFT, etc.) 
are contained in Ralph's PhD thesis, available on the web at URL 
www.cecam.fr

Concerning J, the best way to calculate it is by constrained DFT. What 
ought to be done is to calculate the energy difference between 
configurations in which the magnetic moments on neighboring atoms are 
constrained to different directions, and then fit the results to kind 
of a Heisenberg model. Again, constrained DFT used to be implemented in 
PWscf in the past, using the penalty function technique that is 
described e.g. in Ralph's thesis. If it is no longer implemented, it 
would be very easy to re-implement it.

Hope this helps
Yours, Stefano B

On Oct 20, 2004, at 10:04 AM, xianghjun wrote:

> xianghjun wrote:
>
>> Dear all:
>>    I want to deal with the non-collinear magnetism systems using 
>> pwnc.x,
>> would you please recommend some references about the implementation 
>> in PWNC?
>> P.S.,  I want to get the exchange parameter J using PWNC, is that 
>> possible?
>>
>>
>> Best regards,
>> xianghjun
>>
>> _______________________________________________
>> Pw_forum mailing list
>> Pw_forum at pwscf.org
>> http://www.democritos.it/mailman/listinfo/pw_forum
>
> An other related question is:
> Can PWNC deal with spin spirals?
> I have examined the input help file  "INPUT_NC",
> it seems  that the answer is "no".
> Am I right?
> Best regards,
> xianghjun
>
>
> _______________________________________________
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> Pw_forum at pwscf.org
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>
---
Stefano Baroni    ---  SISSA  &  DEMOCRITOS National Simulation Center
via Beirut 2-4 34014 Trieste Grignano / [+39] 040 3787 406 (tel) -528 
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