GMX-CURRENT(1)

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

💖 GMX-CURRENT(1) 💖

ok so this is a page from the GROMACS manual, bestie — it's gmx-current, and it lives in section 1. Let's get into it ✨

🌸 NAME 🌸

gmx-current — the tool that calculates dielectric constants and the current autocorrelation function. no cap.

🦋 SYNOPSIS 🦋

gmx current [-s [<.tpr/.gro/...>]] [-n [<.ndx>]] [-f [<.xtc/.trr/...>]]
            [-o [<.xvg>]] [-caf [<.xvg>]] [-dsp [<.xvg>]]
            [-md [<.xvg>]] [-mj [<.xvg>]] [-mc [<.xvg>]] [-b <time>]
            [-e <time>] [-dt <time>] [-[no]w] [-xvg <enum>]
            [-sh <int>] [-[no]nojump] [-eps <real>] [-bfit <real>]
            [-efit <real>] [-bvit <real>] [-evit <real>]
            [-temp <real>]

✨ DESCRIPTION ✨

okay so gmx current is THE girl for computing the current autocorrelation function, the correlation of the rotational and translational dipole moment of your system, and the static dielectric constant that falls out of it 🫶 To get a reasonable result, the index group has to be neutral — that part is not optional, it's giving non-negotiable 💅

And like… the routine can also pull the static conductivity out of the current autocorrelation function, if velocities are given. And bonus: an Einstein-Helfand fit can be used to get the static conductivity too 🔥

The -caf flag is for the output of the current autocorrelation function, and -mc writes the correlation of the rotational and translational part of the dipole moment into the corresponding file. But heads up bestie — that -mc option is only available for trajectories containing velocities 🙈

Options -sh and -tr are the ones responsible for the averaging and integration of the autocorrelation functions. Since the averaging proceeds by shifting the starting point through the trajectory, you can modify that shift with -sh so you actually get the choice of uncorrelated starting points 👑

And towards the end, the statistical inaccuracy grows — so integrating the correlation function only yields reliable values until a certain point, which depends on the number of frames. The option -tr is what controls the region of the integral that gets taken into account for calculating the static dielectric constant.

Option -temp sets the temperature required for the computation of the static dielectric constant 🌡️

Option -eps controls the dielectric constant of the surrounding medium — for simulations using a Reaction Field or dipole corrections of the Ewald summation. (-eps=0 corresponds to tin-foil boundary conditions ✨).

-[no]nojump unfolds the coordinates to allow free diffusion. This is required to get a continuous translational dipole moment, which is required for the Einstein-Helfand fit 🧚 The results from the fit let you determine the dielectric constant for a system of charged molecules. But lowkey? It's also possible to extract the dielectric constant from the fluctuations of the total dipole moment in folded coordinates. However — that option has to be used with care, since only very short time spans fulfill the approximation that the density of the molecules is approximately constant and the averages are already converged 😭 To be on the safe side, the dielectric constant should be calculated with the help of the Einstein-Helfand method for the translational part of the dielectric constant. periodt.

🎀 OPTIONS 🎀

💾 Options to specify input files:

  • -s [<.tpr/.gro/...>] (topol.tpr) — Structure+mass(db): tpr gro g96 pdb brk ent
  • -n [<.ndx>] (index.ndx) (Optional) — Index file
  • -f [<.xtc/.trr/...>] (traj.xtc) — Trajectory: xtc trr cpt gro g96 pdb tng h5md

📝 Options to specify output files:

  • -o [<.xvg>] (current.xvg) — xvgr/xmgr file
  • -caf [<.xvg>] (caf.xvg) (Optional) — xvgr/xmgr file
  • -dsp [<.xvg>] (dsp.xvg) — xvgr/xmgr file
  • -md [<.xvg>] (md.xvg) — xvgr/xmgr file
  • -mj [<.xvg>] (mj.xvg) — xvgr/xmgr file
  • -mc [<.xvg>] (mc.xvg) (Optional) — 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
  • -sh <int> (1000) — Shift of the frames for averaging the correlation functions and the mean-square displacement.
  • -[no]nojump (yes) — Removes jumps of atoms across the box.
  • -eps <real> (0) — Dielectric constant of the surrounding medium. The value zero corresponds to infinity (tin-foil boundary conditions).
  • -bfit <real> (100) — Begin of the fit of the straight line to the MSD of the translational fraction of the dipole moment.
  • -efit <real> (400) — End of the fit of the straight line to the MSD of the translational fraction of the dipole moment.
  • -bvit <real> (0.5) — Begin of the fit of the current autocorrelation function to a*t^b.
  • -evit <real> (5) — End of the fit of the current autocorrelation function to a*t^b.
  • -temp <real> (300) — Temperature for calculating epsilon.

👀 SEE ALSO 👀

More info about GROMACS is available at http://www.gromacs.org/ (the original page breaks that URL across lines, but you get it bestie 🫶).

2026, GROMACS development team

and that's the whole vibe check, bestie 💖 this was GMX-CURRENT(1) from GROMACS version 2026.4, dated Oct 02, 2026 — go slay your dielectric constants, ily 🎀✨🦋

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