[CP2K-user] [CP2K:22038] Rotational modes of methanol have high frequencies (> 550 cm-1), and they do not look like rotations

[Torstein Fjermestad]

CP1K version: 2023.1

Dear all, 

I am doing a frequency calculation on a methanol molecule in a cubic unit 
cell of length 20.0 Å, using the M06 functional. 
I have noticed that the three lowest frequencies, corresponding to 
rotational modes, are very high (> 550 cm-1, see table below). I am aware 
that the frequencies of rotational modes will not be exactly zero in a 
numerical calculation, but I was at least expecting frequencies lower than 
100 cm-1 for these modes. 
Furthermore, the modes do not look like rotations, but rather like angle 
bending and twisting of a torsion. 

I investigated the convergence with respect to the following parameters:
EPS_SCF, EPS_DEFAULT, CUTOFF, REL_CUTOFF (see table below), but it had a 
negligible effect on the vibrational frequencies. 
Are there other crucial parameters that may affect the vibrational 
frequencies that I am not aware of?
Please find the output files attached (The input is given at the start of 
the *.out files). 
Thanks in advance for your help. 

Best regards,
Torstein



[image: Screenshot 2026-01-08 204106.png]



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