[CP2K-user] [CP2K:22278] Spin polarized calculation with xTB

Dmitry Ryndyk dmitry.ryndyk at tu-dresden.de
Tue Jun 9 11:47:02 UTC 2026
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I made new tests, sorry for any misunderstanding. I used smearing 
incorrectly. 
As I see now, tblite works with UKS and gives some results that look 
reasonable.

Thank you for your comments,
Dmitry

Dmitry Ryndyk schrieb am Dienstag, 9. Juni 2026 um 11:36:30 UTC+2:

> 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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