Troubles with getting raman spectra from MD

[DmitryZ]

Dear colleagues!

 

I recently started working with the cp2k. Currently, I'm learning to 
calculate Raman spectra through MD (using TRAVIS).


The first system was a water molecule placed in the center of a box 8x8x8 
angstroms. The temperature is 400K, the MD step is 0.5fs, the number of 
steps is 4000. The positions of the Raman frequencies agree well with the 
experimental values, but there is also an intensity in the region of small 
wave numbers (below 250 cm-1).

The second system was a PbCl2 molecule in a box of the same dimensions. The 
temperature is 1000K, the MD step is 7.5fs, the number of steps is 4000. 
There are no peaks on the calculated Raman spectrum.

 

In both cases, the intensity of the applied field was 5.0E-04 and the 
JACOBI method was used in LOCALIZE section. I used the DZVP-GTH basis sets 
and the PBE functional. 

 

<https://lh3.googleusercontent.com/-nYPgnqouXbI/WoMFfwggBKI/AAAAAAAAAEo/QJzNM32I8bUmW_xXxSIGrdpxkhH1ufpywCLcBGAs/s1600/1.jpg>I 
have two questions, the answers to which I hope to get with your help

1) What is the reason for the water spectrum features below 250cm-1?

2) What could be the reason for the lack of peaks in PbCl2 Raman 
spectrum? Input files are attached.


Regards, 

Dmitry


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