[QE-users] Computing frozen phonons for a ferromagnetic system

[Pietro Delugas]

Hi

  the starting_magnetization is specified per species not per site, this 
may be sometime not very practical, but in your case warrants  that the 
supercell is initialized in the same way as the  bulk one. Consider also 
that if the ferromagnetic solution is stable, the final density and 
magnetization are not very sensitive to the specific initialization, the 
starting_magnetization only breaks the symmetry between the two 
polarization and defines which is the majority spin.

Contrains instead affect the energy with an additive term that depends 
on the deviation from the constaint, and as you are going to do finite 
differences between displaced systems, where you might actually expect 
some small variation of the local magnetizations this could influence 
you results.

hope this helps - regards

Pietro

On 28/07/20 00:35, Hien Vo wrote:
>
> Hi all,
>
> I’m trying to compute phonons by the frozen phonon approach of a 
> ferromagnetic system. I’m not exactly sure how to go about it.
>
> I’m planning to converge a unit cell of 20 atoms using the 
> starting_magnetization option. Then I will use Phonopy to generate a 
> set of 80-atom supercells with finite displacements and run pwscf on 
> those. How should I treat magnetization in these supercells? I’m 
> concerned that if I use starting_magnetization again, the systems 
> might converge to different ‘magnetic moment per site’ values.
>
> I’m thinking of trying the constrained_magnetization=’atomic’ option 
> and constrain each atomic magnetic moment to the value achieved in the 
> 20-atom unit cell. Is this the way to go?
>
> Best,
>
> Hien Vo
>
> PhD Student
>
> Chemistry Department | The University of Chicago
>
> Best,
>
> Hien Vo
>
>
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