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

[Łukasz Walewski]

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.
-- 
 _____________________________________________________________________
| Dr. Gerald Mathias                 | Phone : ++49 (0)234-32 22847   |
| Lehrstuhl fuer Theoretische Chemie | Fax   : ++49 (0)234-32 14045   |
| Ruhr-Universitaet Bochum           | gerald.mathias at theochem.rub.de |
| D-44780 Bochum                     | http://www.theochem.rub.de/    |
|_____________________________________________________________________|
-------------- next part --------------
# constants and conversion factors
# speed of light in cm/s
  define c
  c=2.99792458e10
# atomic units to fs
  define t_au
  t_au = 2.418884326555e-2
#timestep in fs
 define timestep
# scale of the x values, here ps
# use t_au if you have only the integration step number
 timestep=1.0e-12

# do the Fourier transform
DFT(g0.s0,REAL,NONE,FREQUENCY,MAGNITUDE)

# converting the frequency to wavenumbers
 s1.x=s1.x/timestep /c

# hide input
s0 hidden on

# selecting the viewport and frequency range
view 0.15,0.6,0.85,1.00
world xmin 0
world xmax 20000
# axes labels, colors and final scaling
xaxis  label "frequency (cm\S-1\N)"
yaxis  label "intensity"
AUTOSCALE YAXES
AUTOTICKS