[CP2K-user] [CP2K:17885] Vibrational analysis

[mengchao shi]

Thank you for your reply, it is very useful for me.

在2022年10月16日星期日 UTC+8 00:18:30<Lucas Lodeiro> 写道：

> 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 (<smclu... 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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>>
>

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