[Pw_forum] Constrained Direction of Magnetization

[Gabriele Sclauzero]

Dear Sahar,

On 01/27/2011 10:38 PM, Sahar Mirshamsi wrote:
> Hi pwscf users,
>
> I am trying to do non-collinear calculation and add a penalty functional
> to the Hamiltonian in order to constrain direction of magnetic moment of
> some atoms in my desired direction. So I added these tags to my usual
> input file:
>
> noncolin=.TRUE.
> constrained_magnetization='atomic'
> angle1(i)= desired amount in degree    i=1,ntyp
> angle2(i)= desired amount in degree    i=1,ntyp
> lambda=desired amount

You may need to play a bit with this value. In some cases you might need 
to start with some small value and then restart the run by increasing it 
gradually (this is not done automatically by the code). You should also 
beware of symmetry issues, as stated in the docs.

> as the result, I expect that the code will keep the direction of magnetic
> moments in desired direction and in every step just changes the magnitude
> of magnetization until the convergence achieves, but I see the magnetic
> moment of every atom is changing in both magnitude and direction in every
> step.
>
> 1) Am I missing something in my input file?
How can we say if you do not provide a complete input?

> or the whole procedure is
> different from what I expected?

No, I think it should do what you need and what stated in the 
documentation. The point is that you cannot really "fix" the direction 
of the local magnetization in a PW calculation, but only (try to) 
constrain it. In the code this is implemented with a penalty energy, 
which might not be not the ideal method in some cases.

> 2) How starting_magnetization will be related to this constraining
> process?
> 3) How does code choose the radius of the sphere around every atom for
> calculating the charge and magnetic moment of every atom?
>
> I appreciate any help in finding the answers of these questions.
>
> ______________________________
> Sahar Mirshamsi
> Quantum Theory Project (QTP) and Physics Department,
> University of Florida
>
>
>
>
>
>
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-- 

Gabriele Sclauzero, EPFL SB ITP CSEA
PH H2 462, Station 3, CH-1015 Lausanne