[CP2K-user] [CP2K:16635] Re: Spin polarization and multiplicity in H-abstraction on a SiC surface where total magnetic moment changes

Marcella Iannuzzi marci.akira at gmail.com
Thu Feb 24 13:21:18 UTC 2022

Dear Senja, 

With smearing activated, by default the multiplicity is not conserved.
Have you already tried the keyword


in the section 
CP2K_INPUT <https://manual.cp2k.org/trunk/CP2K_INPUT.html> / FORCE_EVAL 
<https://manual.cp2k.org/trunk/CP2K_INPUT/FORCE_EVAL.html> / DFT 
<https://manual.cp2k.org/trunk/CP2K_INPUT/FORCE_EVAL/DFT.html> / SCF 
<https://manual.cp2k.org/trunk/CP2K_INPUT/FORCE_EVAL/DFT/SCF.html> / SMEAR 


On Thursday, February 24, 2022 at 9:26:37 AM UTC+1 senja.r... at gmail.com 

> Dear CP2K developers and users,
> I have a question regarding spin polarized calculations and the use of the 
> multiplicity and relax_multilplicity tags. 
> I would like to calculate the H-abstraction energy on my Si-terminated 
> 4H-SiC (0001) surface. 
> Initial structure: each Si surface atom has one dangling bond which is 
> passivated by hydrogen atom (non magnetic groundstate, magnet moment = 0).
> Final structure: one Si-H bond is broken, the H atom is moved away from 
> the surface. The dangling bond and H atom now have a spin polarized ground 
> state in which both unbound electrons occupy one spin channel (spin 
> polarized groundstate, magnetic moment = 2).
> I have plotted my results for VASP and CP2K in the attached figure. The 
> nonmagnetic calculations show good overlap (blue and purple curve).
> For vasp, one can fix the total magnetic moment with NUPDOWN = 0/2. If one 
> sets this to 2 and starts with a ferro magnetic initial guess for all atoms 
> (MAGMOM = N*1), the orange curve is retrieved. One can see that the 
> groundstate is nonmagnetic until 3.4A and then becomes ferromagnetic. 
> Additionally, one can not set NUPDOWN and let it relax (red and green curve 
> for two different initial guesses). In this case, VASP is close to the 
> correct transition but not perfect. 
> In CP2K, once I turn on the magnetization with UKS and MAGNETIZATION = 1 
> in the &KIND section, the curves are all over the place and hop in and out 
> of different magnetic states. I tried to tune this with the MULTIPLICITY 
> and RELAX_MULTIPLICITY tag without success. 
> My questions are:
> 1. How can I fix the total magnetic moment so that I could reproduce the 
> orange VASP curve with CP2K?
> 2. What's the influence of the multiplicity on this calculation (I tried 
> the default 1 and the triplet/3 settings). I suppose my system is similar 
> to the O2 example where the Si-dangling bond and H electron are similar to 
> the triplet state.
> 3.What does relax_multiplicity do? It seems to improve some data points 
> (grey vs. brown curve) but not all.
> 4. Which print settings should I use to get an overview of the magnetic 
> moment total (like printed in OSZICAR VASP) and on each atom (comparable to 
> LORBIT = 11 in VASP) 
> I would like to start using CP2K more but need to understand the spin 
> polarization. Can I improve my results to come closer to VASP (or maybe 
> even better)?
> Thank you in advance!
> Best wishes,
> Senja Ramakers (PhD student at Ruhr-Universität Bochum)

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/d4f93141-cf1f-423e-8538-5d4e3d9168a1n%40googlegroups.com.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.cp2k.org/archives/cp2k-user/attachments/20220224/410af254/attachment.htm>

More information about the CP2K-user mailing list