[Pw_forum] about total magnetization convergence

[Cyrille Barreteau]

I fully agree with Nicola.
It is very common in magnetic materials to have several
metastable solutions. For example in fcc iron you can
easily find situations where you calculation converges
towards different solutions depending on very small
changes of initial conditions (or mixing etc..).
I am not so familiar with Ni but maybe there is
a similar behavior.

As suggested by Nicola it could be a good idea to do
some "fixed spin moment" calculation for several values of
the moment and find the minima in the E(M) curve.

  cyrille


Le Jeu 15 juin 2006 20:05, Nicola Marzari a écrit :
>
>
> One possibility is that you are converging to different self-consistent
> states - in a spin-polarized calculation this is fairly common - and the
> energy differences between different magnetizations could be small.
>
> So, what you are seeing might not be an erratic behavior, but the fact
> that there are two or more potential energy surfaces very close to each
> other, and corresponding to different magnetizations.
>
> As always, check carefully k-point sampling and the amount of degauss
> used (around 0.01-0.02 Ry, for this case). Note that you can fix the tot
> amgnetization in the code, if needed.
>
> 			nicola
>
>
> aarti srirangarajan wrote:
>> Dear all,
>>
>> I am doing a spin polarised slab calculation with vacuum layers for Ni.
>> I have a problem here with the total magnetization values. I hv
>> performed
>> calculations with 7 7 1 , 9 9 1 and 11 11 1 and 13 13 1 k-point meshes
>> for
>> various surfaces  and
>> the total magnetisation changes very erratically. The values are not
>> converging. Although the Final energies are converging very well.
>> Also the difference b/w the Total and abs. magnetisation is of the
>> order
>> of 2 bohrs. Could anyone help me with this?
>>
>> thank you
>> Aarti
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>
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