gmx-dielectric - Man Page

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>]

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 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

gmx(1)

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

2026, GROMACS development team

gmx(1).