[CP2K-user] [CP2K:21287] frequencies

[Frederick Stein]

Hi Sihem,
I checked your geometry and your forces. Is your system expected to be 
planar? If yes, try to set the y-coordinates of your atoms to 0.
Generally, a vibrational analysis requires tighter thresholds. Your forces 
need to have an higher accuracy than the force differences which are used 
by CP2K to run the analysis. With your value of the DX parameter, I see 
from your force differences that you need an accuracy significantly better 
than 1e-4 to 1e-5, i.e. at least 1e-6 to 1e-7. Especially an EPS_SCF of 
1e-6 is usually to high. Please double-check the convergence of the 
parameters EPS_DEFAULT, EPS_SCF and CUTOFF and in your case maybe even the 
box-size in x-direction.
Best,
Frederick

Sihem AZIZI schrieb am Samstag, 15. März 2025 um 14:53:30 UTC+1:

> Dear Jürg and Frederick, Thank you very much for your reply. Yes, I 
> perform a geometry optimization calculation before starting the frequency 
> calculation, optimizing all the parameters. In response to Jürg : I perform 
> an optimization calculation on an isolated organic molecule, setting 
> PERIODIC NONE and using POISSON_SOLVER ANALYTIC, followed by a frequency 
> calculation.
> For now, I'm only studying the isolated molecule; the periodic system will 
> follow as soon as I understand how it works.  
> The coordinates in the input file are obtained from a geometry 
> optimization calculation performed with Gaussian. I took the coordinates 
> as-is from the Gaussian output file.
> I have attached all the files. Thanks again for your help.
> Sihem 
> On Friday, March 14, 2025 at 10:49:02 AM UTC+1 Jürg Hutter wrote:
>
>> Hi 
>>
>> are you running using a supercell (periodic) or have you set 
>> PERIODIC NONE for CELL and POISSON Solver ? 
>>
>> Default is to only remove 3 translations in periodic calculations, 
>> no rotations will be removed (3 further frequencies). 
>>
>> regards 
>> JH 
>>
>> ________________________________________ 
>> From: cp... at googlegroups.com <cp... at googlegroups.com> on behalf of Sihem 
>> AZIZI <sihema... at gmail.com> 
>> Sent: Thursday, March 13, 2025 10:26 PM 
>> To: cp2k 
>> Subject: [CP2K:21281] frequencies 
>>
>> Dear all, 
>> I'm trying to calculate the frequencies of an organic molecule, and each 
>> time I get two or three negative values. I don't understand why. When I do 
>> the same thing with Gaussian, all the values ​​are positive. Can you help 
>> me? Thank you. 
>>
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>>
>

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