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

[Armando Navarro Vázquez]

A convenient method to supress low ( or high frequencies ) is to use wavelet 
transform. Maybe is of interest to your problem.
> Dnia 2008-05-15, czw o godzinie 01:12 +0200, Łukasz Walewski pisze:
> > Dnia 2008-05-14, śro o godzinie 18:10 +0200, Łukasz Walewski pisze:
> > > Hi,
> > >
> > > This question has been raised already
> > > (http://cpmd.org/mailman/htdig/cpmd-list/2006-November/003574.html) but
> > > is still left unanswered: how to calculate the power spectrum of the
> > > electronic degrees of freedom, i.e. Eq. (47) from
> > > http://www.theochem.ruhr-uni-bochum.de/research/marx/marx.pdf
> > >
> > > The problem is how to get the velocity autocorrelation function of the
> > > electronic DOF from CPMD simulation ?
> > >
> > > Regards,
> > > Lukasz
> >
> > Lukasz,
> >
> > you can easily do that in xmgrace. load your electronic kinetic energy
> > as a
> > single set and do a Fourier transform of it.
> > this is easily done with the little skript attached.
> > maybe you have to modify the timestep. i've based it on the
> > data you have posted recently.
> > you can use it as
> >
> > > xmgrace -batch power.xmb elec-ekin.dat
> >
> > or however your data file is called.
> > have fun,
> > gerald
> >
> > PS: i've just seen that axel was quicker. i've trouble with the mailing
> > list accepting my mails, so i address you directly. if you want, just
> > forward this
> > mail to the list.
>
> Dear Gerald, Axel,
>
> Yes. The Fourier transform of EKINC gives some hints about the power
> spectrum but has a lot of noise in the low frequency region (that is of
> my particular interest). That's why I wanted to know how to get the
> exact power spectrum or alternatively how to "temperature correct" it.
> One can subtract the mean value of the signal in order to get rid of the
> 0th frequency but this does not take all noise away.
>
> Autocorrelating EKINC before FT does not work for me since the ACF in
> the case of systematic noisy drift is almost linear decay with only one
> frequency close to 0 (or couple of them).
>
> Regards,
> Lukasz
>
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-- 
Dr. Armando Navarro-Vázquez
Departamento de Química Orgánica
Phone:34981563100 ext 16231
Universidade de Santiago de Compostela
http://galileo.usc.es/~armando