[gmx-users] g_current

[Florian Dommert]

Hi,

 I would say the problem is too less statistics. In the paper where the tool
was introduced, a simulation of 100ns has been performed in order to
achieved sufficient sampling. 

The order of magnitude is given due to the units. 

Simulate for a longer time to get rid of the noise. Calculating these kind
of correlations functions is really not a simple task.

Schroeder et al. have published an article about fitting of dielectric
spectra for ionic liquids, where this problem is discussed in detail.

Cheers,
Flo

> -----Original Message-----
> From: gmx-users-bounces at gromacs.org [mailto:gmx-users-
> bounces at gromacs.org] On Behalf Of Nilesh Dhumal
> Sent: Monday, July 08, 2013 10:32 PM
> To: gmx-users at gromacs.org
> Subject: [gmx-users] g_current
> 
> Hello,
> I am calculating the correlation of rotational and translation dipole
> moment of ionic liquids. I run the 1 ns simulation and saved the
> trajectory at 1 fs.
> 
> g_current -f md.trr -s md.tpr -n index.ndx -mc
> 
> I selected "system" group.
> 
> Here I pasted the initial j(t) vales and the final value is infinity.
> 
> # This file was created Sun Jul  7 20:51:59 2013
> # by the following command:
> # g_current -f md.trr -s md.tpr -e 10.0 -mc
> #
> # g_current is part of G R O M A C S:
> #
> # Gallium Rubidium Oxygen Manganese Argon Carbon Silicon
> #
> @    title "M\sD\N - current  autocorrelation function"
> @    xaxis  label "Time (ps)"
> @    yaxis  label "< M\sD\N (0)\c7\CJ(t) >  (e nm/ps)\S2"
> @TYPE xy
> # time   M_D(0) J(t) acf         Integral acf
> 0.000   -5.20584e-15             0
> 0.001   -6.97466e-15    -1.42702e-17
> 0.002   -6.97511e-15    -5.25081e-17
> 0.003   -6.97474e-15    -9.07484e-17
> 0.004   -6.97391e-15    -1.28987e-16
> 
> 
> 
> Why final value is infinity? If I do autocorrelation function of these
> values, I get all values 0.
> 
> Why J(t)values are in range of e-15?
> 
> Nilesh
> 
> 
> 
> --
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