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g_dielectric

NAME

g_dielectric - calculates frequency dependent dielectric constants

VERSION 4.6.6

SYNOPSIS

g_dielectric −f dipcorr.xvg −d deriv.xvg −o epsw.xvg −c cole.xvg −[no]h −[no]version −nice int −b time −e time −dt time −[no]w −xvg enum −[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

g_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. The functional forms of the available functions are:

One parameter: y = exp(−a_1 x),

Two parameters: y = a_2 exp(−a_1 x),

Three parameters: y = a_2 exp(−a_1 x) + (1 − a_2) exp(−a_3 x).

Start values for the fit procedure can be given on the command line. 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 dipcorr.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]hno
Print help info and quit

−[no]versionno
Print version 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]wno
View output .xvg, .xpm, .eps and .pdb files

−xvg enum xmgrace
xvg plot formatting: xmgrace, xmgr or none

−[no]fftno
use fast fourier transform for correlation function

−[no]x1yes
use first column as x−axis rather than first data set

−eint real 5
Time 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
epsilon0 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, exp9 or erffit

−nsmooth int 3
Number of points for smoothing

SEE ALSO

gromacs(7)

More information about GROMACS is available at <http://www.gromacs.org/>.

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