[Pw_forum] a question about magnetization

[Gabriele Sclauzero]

Dear Mohsen Modaresi (and Stefano),

Stefano Baroni wrote:
> If what you want is different from what Mother Nature wants (or, rather 
> from the caricature of Mother Nature's willings given by DFT/GGA/etc.) 
> the only way is to use magnetic constraints. They used to be 
> implemented. Don't know what the current situation of the implemenattion 
> is. You can try without constraints to start with ... SB

I can confirm that they are still implemented, though I never explored the functionality 
of all the possible magnetic constraints.
The costraints are implemented by adding a "penalty" magnetic field (see appendix of the 
PhD thesis of Gabriele Cipriani, downloadable from http://www.sissa.it/cm/phd.php), which 
means that you have to chose a parameter lambda to which the penalty energy is proportional.
When you are exactly at the target magnetization the penalty energy (and field) are zero, 
so that the resulting total energy should not depend on lambda.
choosing lambda may be tricky: if it is too small the final magnetization may be far from 
the target one. If too big, the scf cycle might not converge.

If you want to experiment this method on your system please search for 
"constrained_magnetization" in Doc/INPUT_PW.txt and have a look to PW/add_bfield.f90.


HTH


GS


>  
> On Nov 30, 2009, at 7:32 AM, mohsen modaresi wrote:
> 
>> Dear Paolo
>> Thanks for your answer
>> But I want a situation which atoms have different magnetization at the 
>> final,
>> is there any suggestion?
>> Thanks
>>
>> Mohsen Modaresi
>>
>> On Sun, Nov 29, 2009 at 1:19 PM, Paolo Giannozzi 
>> <giannozz at democritos.it <mailto:giannozz at democritos.it>> wrote:
>>
>>
>>     On Nov 29, 2009, at 9:39 , mohsen modaresi wrote:
>>
>>     > 1) A and B have parallel magnetization direction
>>     > 2) A and C have anti parallel magnetization direction
>>     > could i inter this deference in calculation
>>
>>     with an appropriate usage of "starting_magnetization"
>>     you should be able to select between a final state of
>>     type 1) or 2). Energy differences may turn out to be
>>     VERY small, though
>>
>>     Paolo
>>     ---
>>     Paolo Giannozzi, Dept of Physics, University of Udine
>>     via delle Scienze 208, 33100 Udine, Italy
>>     Phone +39-0432-558216, fax +39-0432-558222
>>
>>
>>
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> 
> ---
> Stefano Baroni - SISSA  &  DEMOCRITOS National Simulation Center - Trieste
> http://stefano.baroni.me [+39] 040 3787 406 (tel) -528 (fax) / 
> stefanobaroni (skype)
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| Gabriele Sclauzero, PhD Student                  |
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