[Pw_forum] antiferro

Gabriele Sclauzero sclauzer at sissa.it
Fri Nov 21 15:41:20 CET 2008

ali kazempoor wrote:
> Daer all
> I start the ferromagnetic calculation for the slab of MnAs containing 7 layer,but after
> finishing the run , the spin polarization of Mn atoms in surface rotate in 180
> and make the layer antiferromagnetic ,are this feasible?

Actually I don't know anything about the physics of your system, but since the spin 
polarization in collinear calculations is a scalar between -1 and 1, I would reply yes, it 
is possible to find opposite spin polarization on non equivalent atoms.

 >    starting_magnetization(1) = 3.0,
 >    starting_magnetization(2) = 0.01,

Be careful of your value of starting_magnetization(1)! It must between -1 and 1! I thought 
that the program would perform a check, but I see that this is not the case. You should 
find this warning in your output file:

      Initial potential from superposition of free atoms
      Check: negative starting charge=(component1):   -0.009305
      Check: negative starting charge=(component2): -193.251520

which I don't know if it is later treated properly in the code. So I suggest you to start 
with a correct value of magnetization.

>                      degauss = 0.02 ,

This may be not small enough for spin polarized calculations, please check convergence.

>                      diagonalization=''
>                    mixing_mode = 'plain'
>             electron_maxstep = 300,

you do not need to specify these fields, and you should not unless you know exactly what 
are the consequences. Defaults are usually good

>                    conv_thr = .0001 ,

This looks too small to me. The default is 10^-6, but some people uses even 10^-8




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