[CP2K-user] what it is mean "filed-free run" of wrting the electron density data In the spectrum calculation?

[yan huang]

Hi:
  I want to compute the IR and Raman spectrum. I use input files which are 
given on "brehm-research.de/files/spec_tutorial_2018.pdf". But I don't 
unstand the mean of "field-free run", and how to display in inp file.  I 
guess "field-free run" means the  deleting the module of PERIODIC_EFIELD in 
inp file. It is right?
&PERIODIC_EFIELD
INTENSITY 5.0E-3
POLARISATION 1.0 0.0 0.0
&END PERIODIC_EFIELD
&PRINT
&E_DENSITY_CUBE
STRIDE 1 1 1
FILENAME =result.cube
APPEND
&END
&END PRINT 
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