[CP2K-user] [CP2K:18776] VIBRATIONAL ANALYSIS

[Jürg Hutter]

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: cp2k at googlegroups.com <cp2k at googlegroups.com> on behalf of Hana <holiaei2 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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