[Pw_forum] Non-collinear calculations: magnetic moment relaxation

[Gabriele Sclauzero]

Il giorno 02/dic/2010, alle ore 07.59, Lukashev Pavel ha scritto:

> But now I end up getting another problem. I am trying to impose a constraint on the magnetization angle (i.e. cosine of angle1, theta) by setting:
> constrained_magnetization='atomic direction'

If you do that, then the code will use theta(i) as the target angles (and also starting angles, I think).

> This doesn't seem to work, unless I start with angle1 (theta) being equal for both iron atoms.

I think that the present algorithm doesn't work if theta=90. Was this the case in your input?
You may also need to play a bit with the value of lambda to get convergence.

> When I set them (theta's) different, they do not stay fixed anymore. I attach my input file along with the portion of the final output showing the magnetization angles. I thought that probably I have to constrain the directions separately for each atom, but I did not figure out how to do it. Simply setting 
> constrained_magnetization(1)='atomic direction'
> constrained_magnetization(2)='atomic direction'

constrained_magnetization is not an array, it just sets a global option. You have to use theta(1)=45, theta(2)=-45,... for instance.

> results in error, and I couldn't find in the manual and/or examples any help on setting these constraints separately.
> Any help to resolve this issue is mostly appreciated (i.e. I want to constrain different magnetization directions on different atoms). I couldn't find the solution on PW forum archives either.
> 
> Gabriele, as for your question, I am using version 4.2. And I include non-collinear scheme for this somewhat simple system mostly to test how non-collinearity works with constrained_magnetization, i.e. with fixed theta. I need this for a bit more complicated project I am currently working on.

I think that the constrained magnetization is a seldom used feature and the code perhaps needs some improvements. If you really plan to use it extensively, you might think of some better implementation, or at least some ameliorations. Please have a look in PW/add_bfield.f90, PW/setup.f90, and PW/input.f90, it's all contained there.

HTH

GS

> 
> Thank you,
> 
> Pavel 
> 
> Pavel Lukashev, Ph.D.
> Research Associate
> UNL, Department of Physics & Astronomy
> 208 Theodore Jorgensen Hall
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§ Gabriele Sclauzero, EPFL SB ITP CSEA
   PH H2 462, Station 3, CH-1015 Lausanne

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