[CP2K-user] [CP2K:17290] Re: Spin polarized KS with Relax_multiplicity does not converge

[Marcella Iannuzzi]

Dear Laura

When using diagonalization+smearing the multiplicity is never fixed by 
default. Are you sure that you are fixing the multiplicity?
The relax_multiplicity makes no sense in this case and probably it is only 
creating discontinuous changes in the electronic distribution, which 
prevent the convergence.
Spin polarised systems are notoriously harder to converge.
Often the initial guess has a significant influence on the final result.
In general using mixing it is normal to see lower values in energy along 
the iterative loop, because the densities used to calculate the hamiltonian 
are not single solutions of the diagonalization algorithm.
0.40E+00 for alpha is very large, in particular if there are convergence 
issues

Regards
Marcella


On Friday, July 8, 2022 at 1:37:36 PM UTC+2 Laura Scalfi wrote:

> Dear Cp2k forum, 
>
> We are trying to run a graphene sheet with a Fe defect (containing 1 Fe 
> atom and 4 N atoms, 155 atoms in total), using spin polarized Kohn-Sham 
> (UKS). We managed to run fixed multiplicities of 1, 3 and 5 using the 
> keywords UKS and MULTIPLICITY and the orbital transformation algorithm. 
> However, we would like to let the multiplicity relax using 
> RELAX_MULTIPLICITY keyword and we haven’t been able to make any energy 
> calculation converge yet. 
>
> We are using DIAGONALIZATION instead of OT, with ADDED_MOS 500 and a 
> Fermi-Dirac smearing with temperature 300 K. As of now we succeded to get 
> convergence for DIAGONALIZATION – using the standard algorithm – (I) 
> without UKS, (II) with UKS and a fixed MULTIPLICITY of 1, and (III) with 
> UKS and RELAX_MULTIPLICITY starting from a multiplicity of 1 (but, however 
> large the RELAX_MULTIPLICITY, we did not observe any switching of spin).
>
> Note that, even for the multiplicity 1, the SCF loop converges on a value 
> higher than one found earlier in the loop (see below), and we therefore are 
> not sure whether we can trust this.
>
> ###############################################
>
> SCF WAVEFUNCTION OPTIMIZATION
>
>
> Step Update method Time Convergence Total energy Change
>
>
> ------------------------------------------------------------------------------
>
> 1 NoMix/Diag. 0.40E+00 1.0 0.94554597 -1011.7340994699 -1.01E+03
>
> 2 Broy./Diag. 0.40E+00 1.5 0.98949973 -984.4304450815 2.73E+01
>
> 3 Broy./Diag. 0.40E+00 1.5 1.00114938 -1018.8335907387 -3.44E+01
>
> 4 Broy./Diag. 0.40E+00 1.5 0.75169399 -1001.3444674373 1.75E+01
>
> 5 Broy./Diag. 0.40E+00 1.5 0.71210144 -1019.8272742272 -1.85E+01
>
> 6 Broy./Diag. 0.40E+00 1.4 0.91325270 -1013.4277794778 6.40E+00
>
> *7 Broy./Diag. 0.40E+00 1.4 0.50466440 -1029.6824961219 -1.63E+01*
>
> 8 Broy./Diag. 0.40E+00 1.5 0.33674220 -1021.0650257790 8.62E+00
>
> ...
>
> 40 Broy./Diag. 0.40E+00 1.4 0.00002151 -1017.3149228922 1.08E-04
>
> 41 Broy./Diag. 0.40E+00 1.4 0.00001546 -1017.3151997206 -2.77E-04
>
> *42 Broy./Diag. 0.40E+00 1.4 0.00000072 -1017.3150173627 1.82E-04*
>
>
> *** SCF run converged in 42 steps ***
>
> ########################################################
>
>
> The fixed multiplicity of 3 is very hard to converge (we only managed with 
> specific parameters of Broyden mixing, after 500 iteration steps, and the 
> total spin moment (Mulliken population analysis) was not consistent with 
> the given multiplicity). The RELAX_MULTIPLICITY case, starting from 
> multiplicity 3 or 11, never converges (we set it to 1e-5, but different 
> values up to 0.5 don’t change anything).
>
> We tried Pulay mixing but we got an error of bad conditioning, and 
> Direct_p_mixing seems to worsen the convergence. We also tried using the 
> method OT instead of STANDARD, with CG minimizer or DIIS (as done in a test 
> case with O2), and in all cases it never converged and the OT eigensolver 
> never converged at each step. 
>
> Does anyone can suggest other parameters/methods to use or point out if 
> there is a mistake in our simulations? We attach here a typical input file.
>
> Thank you very much,
>
> Sincerely,
>
> Laura
>

-- 
You received this message because you are subscribed to the Google Groups "cp2k" group.
To unsubscribe from this group and stop receiving emails from it, send an email to cp2k+unsubscribe at googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/cp2k/1b734479-8263-4230-810e-862d82df2387n%40googlegroups.com.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.cp2k.org/archives/cp2k-user/attachments/20220708/d216b227/attachment-0001.htm>