.TH g_dielectric 1 "Mon 4 Apr 2011" "" "GROMACS suite, VERSION 4.5.4-dev-20110404-bc5695c"
.SH NAME
g_dielectric - calculates frequency dependent dielectric constants

.B VERSION 4.5.4-dev-20110404-bc5695c
.SH SYNOPSIS
\f3g_dielectric\fP
.BI "\-f" " dipcorr.xvg "
.BI "\-d" " deriv.xvg "
.BI "\-o" " epsw.xvg "
.BI "\-c" " cole.xvg "
.BI "\-[no]h" ""
.BI "\-[no]version" ""
.BI "\-nice" " int "
.BI "\-b" " time "
.BI "\-e" " time "
.BI "\-dt" " time "
.BI "\-[no]w" ""
.BI "\-xvg" " enum "
.BI "\-[no]fft" ""
.BI "\-[no]x1" ""
.BI "\-eint" " real "
.BI "\-bfit" " real "
.BI "\-efit" " real "
.BI "\-tail" " real "
.BI "\-A" " real "
.BI "\-tau1" " real "
.BI "\-tau2" " real "
.BI "\-eps0" " real "
.BI "\-epsRF" " real "
.BI "\-fix" " int "
.BI "\-ffn" " enum "
.BI "\-nsmooth" " int "
.SH DESCRIPTION
\&\fB g_dielectric\fR calculates frequency dependent dielectric constants
\&from the autocorrelation function of the total dipole moment in
\&your simulation. This ACF can be generated by \fB g_dipoles\fR.
\&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 \fB \-fix\fR
\&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.
.SH FILES
.BI "\-f" " dipcorr.xvg" 
.B Input
 xvgr/xmgr file 

.BI "\-d" " deriv.xvg" 
.B Output
 xvgr/xmgr file 

.BI "\-o" " epsw.xvg" 
.B Output
 xvgr/xmgr file 

.BI "\-c" " cole.xvg" 
.B Output
 xvgr/xmgr file 

.SH OTHER OPTIONS
.BI "\-[no]h"  "no    "
 Print help info and quit

.BI "\-[no]version"  "no    "
 Print version info and quit

.BI "\-nice"  " int" " 19" 
 Set the nicelevel

.BI "\-b"  " time" " 0     " 
 First frame (ps) to read from trajectory

.BI "\-e"  " time" " 0     " 
 Last frame (ps) to read from trajectory

.BI "\-dt"  " time" " 0     " 
 Only use frame when t MOD dt = first time (ps)

.BI "\-[no]w"  "no    "
 View output \fB .xvg\fR, \fB .xpm\fR, \fB .eps\fR and \fB .pdb\fR files

.BI "\-xvg"  " enum" " xmgrace" 
 xvg plot formatting: \fB xmgrace\fR, \fB xmgr\fR or \fB none\fR

.BI "\-[no]fft"  "no    "
 use fast fourier transform for correlation function

.BI "\-[no]x1"  "yes   "
 use first column as \fI x\fR\-axis rather than first data set

.BI "\-eint"  " real" " 5     " 
 Time to end the integration of the data and start to use the fit

.BI "\-bfit"  " real" " 5     " 
 Begin time of fit

.BI "\-efit"  " real" " 500   " 
 End time of fit

.BI "\-tail"  " real" " 500   " 
 Length of function including data and tail from fit

.BI "\-A"  " real" " 0.5   " 
 Start value for fit parameter A

.BI "\-tau1"  " real" " 10    " 
 Start value for fit parameter tau1

.BI "\-tau2"  " real" " 1     " 
 Start value for fit parameter tau2

.BI "\-eps0"  " real" " 80    " 
 epsilon0 of your liquid

.BI "\-epsRF"  " real" " 78.5  " 
 epsilon of the reaction field used in your simulation. A value of 0 means infinity.

.BI "\-fix"  " int" " 0" 
 Fix parameters at their start values, A (2), tau1 (1), or tau2 (4)

.BI "\-ffn"  " enum" " none" 
 Fit function: \fB none\fR, \fB exp\fR, \fB aexp\fR, \fB exp_exp\fR, \fB vac\fR, \fB exp5\fR, \fB exp7\fR, \fB exp9\fR or \fB erffit\fR

.BI "\-nsmooth"  " int" " 3" 
 Number of points for smoothing

.SH SEE ALSO
.BR gromacs(7)

More information about \fBGROMACS\fR is available at <\fIhttp://www.gromacs.org/\fR>.