g_dielectric(1) 				 GROMACS suite, VERSION 4.5.4-dev-20110404-bc5695c				   g_dielectric(1)

NAME

       g_dielectric - calculates frequency dependent dielectric constants

       VERSION 4.5.4-dev-20110404-bc5695c

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 sim-
       ulation. 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 parameter:	 y = Exp[-a1 x],

       Two parameters:	 y = a2 Exp[-a1 x],

       Three parameters: y = a2 Exp[-a1 x] + (1 - a2) Exp[-a3 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 deriva-
       tive  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/>.

								  Mon 4 Apr 2011						   g_dielectric(1)