[CP2K:3561] Re: Is it possible to study/converge magnetic surfaces? repost..

Valerio Bellini valerio... at unimore.it
Wed Oct 26 16:08:11 CEST 2011


Il 26/10/11 15.30, marci ha scritto:
> Dear  Valerio,
>
> I tried your system, 5x5 Ni(111) slab, and I could converge the
> electronic structure by using more or less the same settings that were
> in your input.
> It needs many iterations and the energy keeps oscillating for a long
> time before the algorithm can find a good minimum.
> However, what is really annoying, is that at the end the electrons are
> redistributed between the two spins in such a way that the final
> magnetization is zero, in spite of the fact that the initial guess had
> a high multiplicity.
> It seems that with the present settings and system size, the algorithm
> finds a minimum with no magnetization, and this should be also the
> reason why starting from a magnetization different from zero it takes
> such a long time to converge.
> It is possible that one problem is the size of the system. One should
> check larger boxes to verify that.
> What I can tell for sure is that the optimization of the bulk (216
> atoms) electronic structure, gives the expected magnetization (~0.6
> magneton per unit cell) by using more or less the same SCF set up.
>
> best
> marcella


Dear Marcella,
Thank you for the answer.
Two comments:
1) I did calculation for the same system, using Gamma point only, with 
another code (VASP),
and the total magnetic moment of the cell relaxed to around 86 bohr 
magneton.
With a better multiplicity guess I thought convergence might be easier, 
but it was
not the case.
If I try 87 as multiplicity and I run more than 500 iterations with 
Broyden,
the system converges using Diagonalization+Broyden up to 0.005 Hartree,
but as said in the previous e-mail, the magnetic moments are not equal 
for different atoms
in the same plane, so the system in reality is far from convergence.
Could I ask you how many iterations did it take to you?
2) I do not understand how you could get a non-magnetic solution.
If you impose the multiplicity to some value, and you don't allow 
relaxation of it
(using the keyword, RELAX_MULTIPLICITY) the multiplicity of the system 
should remain
constant (like in a fixed spin moment calculation).
So this means that you inserted that flag in the input file, is that 
correct?
thanks,
Valerio




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