GMX-DIELECTRIC(1)

📦
version 2026.4 · 8 versions
, in nixpkgs unstable, ubuntu stonking

🦋 gmx-dielectric — the girlies' guide ✨

okay bestie, welcome to the GROMACS manual, page gmx-dielectric(1). if you wannna know how to get frequency dependent dielectric constants, you are so in the right place. 💖 no cap.

💅 NAME 💅

gmx-dielectric — Calculate frequency dependent dielectric constants. that's the whole job. she's booked, she's busy, she's serving physics. 🔥

🌸 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>]

look at her. all those flags. iconic. ✨

🎀 DESCRIPTION 🎀

so here's the tea, bestie. gmx dielectric calculates frequency dependent dielectric constants from the autocorrelation function of the total dipole moment in your simulation. it's giving "I did the sim, now I want the vibes."

and where do you get that ACF from? not me forgetting — it's right there: this ACF can be generated by gmx dipoles. 🫶

the functional forms of the available functions are, and yes you need all of them:

  • 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).

three flavors. one for each mood. 💅

start values for the fit procedure? you can hand those over on the command line, queen. it is also possible to fix parameters at their start value, and for that you use -fix with the number of the parameter you want to fix. periodt.

okay so three output files get generated, and each one has a job:

  1. 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.
  2. the second file contains the real and imaginary parts of the frequency-dependent dielectric constant.
  3. 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.

and here's the cute little factoid: for a pure exponential relaxation (Debye relaxation) the latter plot should be one half of a circle. half a circle. a little rainbow arc. 🌈 that's it, that's the plot.

✨ OPTIONS ✨

🍓 Options to specify input files

  • -f [<.xvg>] (dipcorr.xvg) — xvgr/xmgr file. the input. bring it.

💜 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
not me counting them all just to make sure every single one is here 💀 — they all are. 18 out of 18. we ate.

👑 SEE ALSO 👑

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

2026, GROMACS development team

and that's the whole page, bestie!! go slay your dielectric constants 💖

this has been GROMACS 2026.4, dated Oct 02, 2026, page GMX-DIELECTRIC(1) — ty for coming to my ted talk, mwah 🫶🎀✨

📦 where this page comes from