[CP2K-user] [CP2K:22270] Spin polarized calculation with xTB

[Thomas Kühne]

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

> Am 08.06.2026 um 11:51 schrieb Michael LaCount <lacount.mi 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 <tel:+41%2044%20635%2044%2091><tel:+41%2044%20635%2044%2091> 
>> Institut für Chemie C FAX : ++41 44 635 6838 <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 <tel:+41%2044%20635%2044%2091><tel:+41%2044%20635%2044%2091> 
>> Institut für Chemie C FAX : ++41 44 635 6838 <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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