[CP2K-user] [CP2K:18780] VIBRATIONAL ANALYSIS

[Hana]

Hello Dr.Hutter,

Thanks for your response. In this case, would the rest of the frequencies 
(3N-6) still be reliable? or they are also impacted by the fixed atoms?

Thanks!

On Monday, May 8, 2023 at 2:39:22 AM UTC-5 Jürg Hutter wrote:

> Hi
> If you fix atomic coordinates, your system looses its free translations 
> and rotations.
> For such a system you expect 3N non-zero frequencies.
> regards
> JH
>
> ________________________________________
> From: cp... at googlegroups.com <cp... at googlegroups.com> on behalf of Hana <
> holi... at illinois.edu>
> Sent: Friday, May 5, 2023 5:19 PM
> To: cp2k
> Subject: Re: [CP2K:18774] VIBRATIONAL ANALYSIS
>
> Hello Lucas and Krack,
>
> Thanks for your comments. I have attached my input file (input.txt) for 
> your notice. My system consists of a single ion pair (sys.xyz) with no 
> periodic boundary condition and I use the GAPW method with a 400Ry cutoff 
> (Upon convergence test, this cutoff gave me 1e-4 convergence threshold for 
> the total energy). For the normal mode analysis I fix the atoms of one ion 
> and just study the vibrations of the other one. Please let me know what you 
> think.
>
> Thanks!
>
>
> On Friday, May 5, 2023 at 2:31:52 AM UTC-5 Lucas Lodeiro wrote:
> I put my 2 cents in the possibility that you are running your calculation 
> using PBC, so the normal modes are not projected out to extract the 
> translational and rotational modes. Also you probably use a "low cutoff" so 
> the noise (energy/gradient waves due to plane waves), when the numerical 
> derivatives are calculated through adjacent points, is important... then 
> the frequency of your translational and rotational modes are not close to 
> zero as expected.
>
> Regards - Lucas Lodeiro
>
> El jue, 4 may 2023 a las 12:36, Hana (<holi... at illinois.edu>) escribió:
> Hello,
>
> I am trying to obtain the normal modes of my gaseous system which contains 
> a molecule (N atoms). First I optimize the geometry of my system with a 
> MAX_FORCE threshold of 0.0005. Second, in a further calculation, I use the 
> following setting:
>
> &VIBRATIONAL_ANALYSIS
> INTENSITIES
> NPROC_REP 256
> DX 0.001
> &PRINT
> &PROGRAM_RUN_INFO ON
> &END
> &END
> &END
>
> I get 3N frequency modes all of which are nonzero. However, I expect the 
> analysis to exclude the rotation and translation and return zeros for the 
> first six modes. Is there any explanation for this? Here is the output 
> (cm^-1) for the first six modes: 26.89, 30.12, 36.90, 55.93, 68.51, 90.65
>
> Thanks!
>
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