[CP2K-user] [CP2K:22277] Spin polarized calculation with xTB

[Dmitry Ryndyk]

Oh!
Thank you!
I forgot to use FIXED_MAGNETIC_MOMENT with SMEAR.

Best wishes,
Dmitry
Jürg Hutter schrieb am Dienstag, 9. Juni 2026 um 11:21:58 UTC+2:

> Hi
> 1) The implemented xTB Hamiltonians don't have a spin dependence.
> You will always get the same orbital energies for alpha and beta electrons.
> 2) Occupation of the orbital levels depends on a combination of input 
> parameters.
> a) No smearing: Number of alpha and beta electrons is determined from the 
> Multiplicity keyword.
> b) With smearing: default is a single Fermi energy and electrons are 
> allowed to move from alpha
> to beta. This is default because this is what most people want for DFT 
> Mermin functional calculations.
> If you want to keep the number of electrons to be fixed, you need to 
> specify
> FIXED_MAGNETIC_MOMENT 2
> This together with a FD temperature of 300 is the default in tblite (if 
> I'm correct).
>
> regards
> JH
>
> ________________________________________
> From: cp... at googlegroups.com <cp... at googlegroups.com> on behalf of Dmitry 
> Ryndyk <dmitry... at tu-dresden.de>
> Sent: Tuesday, June 9, 2026 7:23 AM
> To: cp2k
> Subject: Re: [CP2K:22273] Spin polarized calculation with xTB
>
> Dear Jürg, Michael, Thomas,
> Thank you for the answers. I use the master git branch, and the UKS tblite 
> simply doesn't work as UKS. I hope to get a reply from someone who cares 
> about tblite integration into CP2K just now.
>
> But meanwhile, I do not understand the internal spin-dependent now. Please 
> have a look at the attachment. I tried
> Multiplicity=3 and got a strange result. There is no spin difference at 
> the end!
> And it has nothing to do with xTB; the same is for DFT PBE.
> Only with OT do I get the expected result.
> What do I not understand?
>
> Thank you in advance,
> Dmitry
>
> Thomas Kühne schrieb am Dienstag, 9. Juni 2026 um 00:30:36 UTC+2:
> Hi everybody,
>
> there have been some recent new developments. In conjunction with tblite 
> 0.6.0
> CP2K now supports GFN2 for periodic systems incl. k-points and via analytic
> gradients and stress tensor for RKS and UKS. Have a look at the recent 
> preprint,
> as well as the recent regtests and 
> https://github.com/DCM-Uni-Paderborn/Periodic-GFN2-Benchmarks
> for representative sample inputs.
>
> Greetings,
> Thomas
>
> <https://chemrxiv.org/doi/abs/10.26434/chemrxiv.15003939/v1>
> chemrxiv.org<https://chemrxiv.org/doi/abs/10.26434/chemrxiv.15003939/v1>
> [X]<https://chemrxiv.org/doi/abs/10.26434/chemrxiv.15003939/v1>
>
>
> Am 08.06.2026 um 11:51 schrieb Michael LaCount <lacou... at gmail.com>:
>
> I looked into this earlier this year.
>
> Tblite does seem to support the spin polarized version (spGFNn) see 
> https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/jcc.27185 "All 
> (sp)GFNn-xTB calculations were performed with the tblite v. 0.3.0 
> development version either as a standalone or in the xtb v. 6.5.1 
> development version." A bit ambiguous but it seems to me to read like 
> tblite supported spGFN-xTB.
>
> But I'll note that I found using LSD with TBLITE GFN1 doesn't work 
> properly (at least in v2026.1) (see 
> https://github.com/cp2k/cp2k/issues/4818 and 
> https://github.com/cp2k/cp2k/pull/4804). Also TBLITE with GFN2 has (or at 
> least had) some odd behavior assigning electrons for nitrogen.
>
> In short, at least as of CP2K 2026.1 there is no way (to my knowledge) to 
> get a proper spGFNn calculation done with CP2K. The best you can do is 
> triplet GFN0/1 using the internal CP2K implementation of XTB.
>
> Best,
> Michael
>
> On Monday, June 8, 2026 at 7:12:08 AM UTC-7 Jürg Hutter wrote:
> Hi
>
> This extension is not included in the CP2K native gfn0/1 xTB Hamiltonians.
>
> I don't know if it is available through tblite, but most likely it has to 
> be triggered by a
> keyword and defaults to the original spinless Hamiltonian.
> Probably this keyword is not yet accessible through the CP2K input?
>
> best regards
> JH
>
> ________________________________________
> From: cp... at googlegroups.com <cp... at googlegroups.com> on behalf of Dmitry 
> Ryndyk <dmitry... at tu-dresden.de>
> Sent: Monday, June 8, 2026 3:36 PM
> To: cp2k
> Subject: Re: [CP2K:22267] Spin polarized calculation with xTB
>
> Dear all,
>
> What is going on at present?
>
> The xTB site<
> https://xtb-docs.readthedocs.io/en/latest/spgfn.html#spgfnn-xtb> states 
> that spin-polarized calculations with tblite are possible, and 
> spin-dependent Hamiltonians are described in the 2023 paper<
> https://onlinelibrary.wiley.com/doi/10.1002/jcc.27185>.
>
> Moreover, at the CP2K site<
> https://manual.cp2k.org/trunk/CP2K_INPUT/FORCE_EVAL/DFT/QS/XTB/TBLITE.html>, 
> it is written:
> Spin-polarized CP2K/tblite calculations are selected with the regular 
> DFT/UKS keyword or its LSD/SPIN_POLARIZED aliases; DFT/MULTIPLICITY sets 
> the number of unpaired electrons. UKS uses tblite’s spin-polarized 
> Hamiltonian.
>
> At the moment, however, it seems to be blocked. One always gets restricted 
> orbitals.
> Any ideas?
>
> Best wishes,
> Dmitry
>
> hut... at chem.uzh.ch schrieb am Freitag, 5. März 2021 um 19:09:23 UTC+1:
> Hi
>
> you can calculate a triplet using UKS. For xTB the results should
> show equal orbital energies for alpha and beta spin, even though
> the occupations will be different.
>
> regards
>
> Juerg
> --------------------------------------------------------------
> Juerg Hutter Phone : ++41 44 635 4491 <+41%2044%20635%2044%2091>
> <tel:+41%2044%20635%2044%2091><tel:+41%2044%20635%2044%2091>
> Institut für Chemie C FAX : ++41 44 635 6838 <+41%2044%20635%2068%2038>
> <tel:+41%2044%20635%2068%2038><tel:+41%2044%20635%2068%2038>
> Universität Zürich E-mail: hut... at chem.uzh.ch
> Winterthurerstrasse 190
> CH-8057 Zürich, Switzerland
> ---------------------------------------------------------------
>
> -----cp... at googlegroups.com wrote: -----
> To: cp... at googlegroups.com
> From: "Pierre-André Cazade"
> Sent by: cp... at googlegroups.com
> Date: 03/05/2021 05:16PM
> Subject: Re: [CP2K:14885] Spin polarized calculation with xTB
>
> Dear Juerg,
>
> It's a very interesting topic. Provided what you described in your reply, 
> is it possible to use xTB for a triplet state? If yes, is it necessary to 
> use UKS, since the Hamiltonian doesn't have spin-dependence?
>
> Regards,
> Pierre
> On Fri, Mar 5, 2021 at 3:42 PM <hut... at chem.uzh.ch> wrote:
> Hi
>
> you can use unrestricted calculations also with xTB. However,
> the xTB Hamiltonian doesn't have a spin dependence. So what you
> get is the same as using a restricted open shell calculation.
> Unrestricted is double the work, but can use OT methods.
> Restricted open shell (ROKS will not work btw) will need
> diagonalization and smearing. What is more efficient in the end
> might depend on your system.
>
> best regards
>
> Juerg Hutter
> --------------------------------------------------------------
> Juerg Hutter Phone : ++41 44 635 4491 <+41%2044%20635%2044%2091>
> <tel:+41%2044%20635%2044%2091><tel:+41%2044%20635%2044%2091>
> Institut für Chemie C FAX : ++41 44 635 6838 <+41%2044%20635%2068%2038>
> <tel:+41%2044%20635%2068%2038><tel:+41%2044%20635%2068%2038>
> Universität Zürich E-mail: hut... at chem.uzh.ch
> Winterthurerstrasse 190
> CH-8057 Zürich, Switzerland
> ---------------------------------------------------------------
>
> -----cp... at googlegroups.com wrote: -----
> To: "cp2k" <cp... at googlegroups.com>
> From: "Mauro Sgroi"
> Sent by: cp... at googlegroups.com
> Date: 03/05/2021 09:33AM
> Subject: [CP2K:14881] Spin polarized calculation with xTB
>
> Dear all,
> I'm trying to understand if it is possible to use xTB to perform spin 
> polarized calculations.
> If yes, which is the right way to proceed?
> Is there an howto to follow?
>
> Thannks a lot and best regards,
> Mauro Sgroi
> Centro Ricerche FIAT
> Italy
>
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