[CP2K-user] [CP2K:16444] Power Spectrum.Help! not zero at 0 cm-1

[Kai]

 Thank you so much for your reply ,Lucas. It's a bulk system. So the value 
of COMVEL_TOL should be set to 0 ?

在2022年1月8日星期六 UTC+8 01:54:31<Lucas Lodeiro> 写道：

> Hi,
>
> The non zero value at zero frequency is typical when you have a 
> system/molecule with translational and rotational movement.
> It is not clear if you are simulating a single molecule (without PBC) or a 
> bulk system (with PBC). For the former case, you could control both with 
> COMVEL_TOL, ANGVEL_TOL and ANGVEL_ZERO keywords. For the second, the 
> angular movement cannot be controlled and just the translation of COM 
> contributes to the zero frequency value. Also, the "natural" band width of 
> the FFT could affect it when a signal is near zero frequency and its tail 
> reaches the zero frequency.
>
> About the MD... a timestep of 10 fs is a very huge one... if you have 
> hydrogens, 0.5 fs is the best, and maybe 1.0 fs could work. Also if you are 
> working with a bulk system, 14 ps of AIMD probably is not sufficient to 
> obtain an equilibrated system in term of structure and in terms of thermal 
> energy.
>
> Regards - Lucas Lodeiro
>
> El vie, 7 ene 2022 a las 0:58, Kai (<liangzi... at gmail.com>) escribió:
>
>> Hello everyone, 
>> I am trying to calculate the vibrational spectrum of an inorganic 
>> cluster using TRAVIS. It's simulated for 14 ps with a CSVR timeconstant of 
>> 1 ps and 10 fs timestep. I think I get the great shape of the  
>> vibrational curve. *But it shows a non zero value at 0 cm-1.*This should 
>> be unreasonable. What should I do?
>> I guess I should remove the 6 macroscopic degrees of freedom (3x 
>> translation, 3x rotation), but how?
>>
>> Please help me.
>> Thanks all.[image: power spectrum.png]
>>
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