[CP2K-user] [CP2K:21980] Re: XAS calculation of an open-shell system

[qing zhou]

Dear Augustin,
Thank you for your suggestions. I will try a different function to continue 
the calculation.
Have a good day!
Best,
Qing_Zhou

在2025年11月13日星期四 UTC+8 17:40:54<Augustin Bussy> 写道：

> Dear Qing Zhou,
>
> Note that TDDFT XAS energies are rarely a close match to experiment, and 
> the whole spectrum generally needs to be blue shifted to match. The 
> difference with respect to experiments increases with heavier elements, as 
> relativistic effects start to have an impact (they are neglected in 
> XAS_TDP, as it is assumed that they only result in a rigid shift of the 
> spectrum). That being said, I do not know what kind of shift to expect for 
> Fe.
>
> All options suggested by Nanchen are relevant and worth testing. 
> Additionally, you can also try using a pre-optimized RI basis such as 
> def2-TZVP-RIFIT (available on the Basis Set Exchange website). The 
> automatically generated RI basis sets are sometimes very large, and that 
> does not help if the system is already numerically brittle.
>
> Best,
> Augustin
>
>
> On Thursday, 13 November 2025 at 10:32:34 UTC+1 Nan Dong wrote:
>
>> Hi qing zhou, 
>>
>> I checked your input and the output, and the spectrum. 
>> In spectrum, there is only one state at 6167.202695 eV, which I would say 
>> it bad but not so bad. 
>> but the only one state should be noticed, which it is due to you set 
>> ENERGY_RANGE 30. The expected Fe 1s around 7000, is out of this range tooo 
>> far. 
>> and I would suggest: 
>> 1. increase the Grid size.  *GRID Fex 500 1000 *
>> 2. decrease the number for searching, *N_SEARCH 5  *
>> Because you only have one Fe here, and calculate its 1s excitations. The 
>> MOs order should be Fe_1s, at the lowest. 
>> 3. increase *RI_REGION* (you can test, ending up to contain all atoms in 
>> the structure) 
>> 4. maybe increase the *ENERGY_RANGE*, I would suggest 1000 or 2000. 
>> since now your first excitation state is 6167, the range should include the 
>> expected states (for Fe 1s 7000 eV approximately). After you improve the 
>> first excitation energy, it can be reduced. 
>>
>> another option, decrease HF portion. PBE0(25%) or B3LYP(25%) might give a 
>> better spectrum, which I preferred for Fe 2p spectrum. 
>>
>> Best, 
>> Nanchen 
>>
>>
>>
>> 在2025年11月13日星期四 UTC+1 06:19:15<qing zhou> 写道：
>>
>>> Dear CP2K users and developers,
>>>
>>> I am using CP2K to calculate the XAS of an open-shell system with a spin 
>>> multiplicity of 2. The OT method was enabled for the SCF calculation to aid 
>>> convergence, and I have set EXCITATIONS OS_SPIN_CONS in the &XAS_TDP 
>>> section. For the functional, I am using a PBE-based functional with 45% 
>>> Hartree-Fock exchange. The def2-TZVP basis set was used for the Fe atom, 
>>> while the DZVP-MOLOPT basis set was used for all other atoms.
>>>
>>> As shown in the output file, the calculation finished without any 
>>> errors, and the SCF converged successfully. However, the excitation 
>>> energies in the resulting spectrum file are obviously incorrect. I recall 
>>> that the energy for the Fe K-edge should be around 7000 eV. Furthermore, 
>>> the spectrum file contains only a single data point.
>>>
>>> I would like to ask what potential issues might exist in my calculation 
>>> setup. How can I adjust my settings to correctly obtain the XAS spectrum 
>>> for this open-shell system?
>>>
>>> I have attached my input (.inp), output (.out), and spectrum files for 
>>> your reference. Thank you for your help!
>>>
>>

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