NAME

       gmx-dielectric - Calculate frequency dependent dielectric constants

SYNOPSIS

          gmx dielectric [-f [<.xvg>]] [-d [<.xvg>]] [-o [<.xvg>]] [-c [<.xvg>]]
                       [-b <time>] [-e <time>] [-dt <time>] [-[no]w]
                       [-xvg <enum>] [-[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

       gmx   dielectric   calculates   frequency   dependent   dielectric   constants   from  the
       autocorrelation function of the total dipole moment in your simulation. This  ACF  can  be
       generated by gmx 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.

OPTIONS

       Options to specify input files:

       -f [<.xvg>] (dipcorr.xvg)
              xvgr/xmgr file

       Options to specify output files:

       -d [<.xvg>] (deriv.xvg)
              xvgr/xmgr file

       -o [<.xvg>] (epsw.xvg)
              xvgr/xmgr file

       -c [<.xvg>] (cole.xvg)
              xvgr/xmgr file

       Other options:

       -b <time> (0)
              Time of first frame to read from trajectory (default unit ps)

       -e <time> (0)
              Time of last frame to read from trajectory (default unit ps)

       -dt <time> (0)
              Only use frame when t MOD dt = first time (default unit ps)

       -[no]w (no)
              View output .xvg, .xpm, .eps and .pdb files

       -xvg <enum> (xmgrace)
              xvg plot formatting: xmgrace, xmgr, none

       -[no]x1 (yes)
              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, exp5, exp7, exp9

       -nsmooth <int> (3)
              Number of points for smoothing

SEE ALSO

       gmx(1)

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

COPYRIGHT

       2018, GROMACS development team