[CP2K-user] [CP2K:17871] Vibrational analysis

[Lucas Lodeiro]

Hello Mengchao,

AFAIK your results are consistent. Of course there are 24 normal modes, and
3 of them are translational ones. CP2K removes the translational modes
before printing the data, you can find this in the CP2K output (search
"VIB| Eigenvectors before removal" and " VIB| Frequencies after removal"),
where the complete set of normal modes and frequencies are printed before
the translational removal. This does not change significantly the results,
so you can think about 21 normal modes and 3 extra translation modes with
zero frequency.
In VASP the translational removal is not done and the low frequency modes
are the translational ones... but at Gamma point they must be zero
frequency. The resulting non zero value is an artifact of the PW rupture of
translational invariance, which is due to the non complete PW basis set
(infinite energy plane wave). As a guess, taking into account that in VASP
the PW cutoff is lower compared with used in CP2K, and PW are used to
wavefunctions, the error due to rupture of translational invariance is
higher in VASP.

Regards - Lucas

El vie, 14 oct 2022 a las 0:42, mengchao shi (<smclucky666 at gmail.com>)
escribió:

> Dear all
>      I want to calculate the atomic frequency of diamond silicon by CP2K.
>      My supercell contains N=8 atoms (a PBC system), and I will get the
> 3N=24 frequencies.
>
>      However, I only get the  21 frequencies,  The frequencies of the
> rotations  are obtained, but the part of translations are not obtained.
>
>      I use the VASP to calcualte the vibrational analysis, I get the 24
> frequencies.
>      I  compare the two results:
>
>  VASP: (unit: cm-1,  24 frequencies )
>  513.100912      513.097046       513.092040
>  461.327377       461.230874     461.217489     461.210747     461.189027
>     461.185948
>  409.422422        409.414429     409.406072    409.397086     409.393930
>    409.387741
>   140.194017       140.189188     140.187673    140.182783     140.175562
>  140.172242
>     0.006451           0.010431         0.055547
>
>   CP2K: (unit: cm-1,  21 frequencies)
>     515.944308    515.944308     515.944308
>     463.042397     463.042397    463.042397    463.042397  463.042397
>    463.042397
>     412.993772     412.993772    412.993772     412.993772  412.993772
> 412.993772
>     139.536054      139.536054    139.536054    139.536054  139.536054
> 139.536054
>
>     The results are similar, but the number is different, how do I get 24
> frequencies by CP2K.
>
>    The part input:
>     "
>      &GLOBAL
>       PROJECT system
>       RUN_TYPE VIBRATIONAL_ANALYSIS
>       PRINT_LEVEL MEDIUM
>    &END GLOBAL
>
>     &VIBRATIONAL_ANALYSIS
>         NPROC_REP 3
>         DX 0.001
>         FULLY_PERIODIC .TRUE.
> &END VIBRATIONAL_ANALYSIS
>        "
>
>        Thank you for your help.
>         Best,
>         Mengchao.
>
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