g_dielectric(1)

NAME

g_dielectric - calculates frequency dependent dielectric constants

SYNOPSIS

g_dielectric  -f  Mtot.xvg  -d deriv.xvg -o epsw.xvg -c cole.xvg -[no]h
-nice int -b time -e time -dt time -[no]w  -[no]xvgr  -[no]fft  -[no]x1
-eint  real  -bfit  real -efit real -tail real -A real -tau1 real -tau2
real -eps0 real -epsRF real -fix int -ffn enum -nsmooth int

DESCRIPTION

dielectric calculates frequency dependent dielectric constants from the autocorrelation function of the total dipole moment in your simulation. This ACF can be generated by g_dipoles. For an estimate of the error you can run g_statistics on the ACF, and use the output thus generated for this program. The functional forms of the available functions are:

One parmeter : y = Exp[-a1 x] Two parmeters : y = a2 Exp[-a1 x] Three parmeter: y = a2 Exp[-a1 x] + (1 - a2) Exp[-a3 x] Startvalues for the fit procedure can be given on the commandline. It is also possible to fix parameters at their start value, use -fix with the number of the parameter you want to fix.

Three output files are generated, the first contains the ACF, an exponential fit to it with 1, 2 or 3 parameters, and the numerical derivative of the combination data/fit. The second file contains the real and imaginary parts of the frequency-dependent dielectric constant, the last gives a plot known as the Cole-Cole plot, in which the imaginary component is plotted as a function of the real component. For a pure exponential relaxation (Debye relaxation) the latter plot should be one half of a circle

FILES

-f Mtot.xvg Input: xvgr/xmgr file
-d deriv.xvg Output: xvgr/xmgr file
-o epsw.xvg Output: xvgr/xmgr file
-c cole.xvg Output: xvgr/xmgr file

OTHER OPTIONS

-[no]h no: Print help info and quit
-nice int 19: Set the nicelevel
-b time 0: First frame (ps) to read from trajectory
-e time 0: Last frame (ps) to read from trajectory
-dt time 0: Only use frame when t MOD dt = first time (ps)
-[no]w no: View output xvg, xpm, eps and pdb files
-[no]xvgr yes: Add specific codes (legends etc.) in the output xvg files for the
xmgrace program
-[no]fft no: use fast fourier transform for correlation function
-[no]x1 yes: use first column as X axis rather than first data set
-eint real 5: Time were to end the integration of the data and start to use the fit
-bfit real 5: Begin time of fit
-efit real 500: End time of fit
-tail real 500: Length of function including data and tail from fit
-A real 0.5: Start value for fit parameter A
-tau1 real 10: Start value for fit parameter tau1
-tau2 real 1: Start value for fit parameter tau2
-eps0 real 80: Epsilon 0 of your liquid
-epsRF real 78.5: Epsilon of the reaction field used in your simulation. A value of 0
means infinity.
-fix int 0: Fix parameters at their start values, A (2), tau1 (1), or tau2 (4)
-ffn enum none: Fit function: none , exp , aexp , exp_exp , vac , exp5 , exp7 or exp9
-nsmooth int 3: Number of points for smoothing

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