---
name: "gmx-dielectric"
section: "1"
platform: "linux"
package: "gromacs-data"
version: "2025.2-1"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/gmx-dielectric"
---

# gmx-dielectric(1)

Calculate frequency dependent dielectric constants

## 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)](/gmx/1.md)**

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

## COPYRIGHT

2025, GROMACS development team