[CPMD-list] Power spectrum of the electronic degrees of freedom

[Axel Kohlmeyer]

On Thu, 15 May 2008, ukasz Walewski wrote:

LW> Dear Gerald, Axel,
LW> 
LW> Yes. The Fourier transform of EKINC gives some hints about the power
LW> spectrum but has a lot of noise in the low frequency region (that is of
LW> my particular interest). That's why I wanted to know how to get the

to converge "slow" processes you have to do a long simulations...

LW> exact power spectrum or alternatively how to "temperature correct" it.
LW> One can subtract the mean value of the signal in order to get rid of the
LW> 0th frequency but this does not take all noise away.
LW> 
LW> Autocorrelating EKINC before FT does not work for me since the ACF in
LW> the case of systematic noisy drift is almost linear decay with only one
LW> frequency close to 0 (or couple of them).

how about a baseline correction of the original data?
also in the case of EKINC you want to discard the first 
bit of the output until it is behaving normal.
since you have a somewhat linear drift you can just 
fit a straight line to the data and subtract it.
that should give you a cleaner spectrum.

experimentalists do these things routinely... (NMR, FT-IR...).

cheers,
   axel.

LW> 
LW> Regards,
LW> Lukasz
LW> 
LW> _______________________________________________
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LW> 

-- 
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Axel Kohlmeyer   akohlmey at cmm.chem.upenn.edu   http://www.cmm.upenn.edu
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