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

# gmx-saltbr(1)

Compute salt bridges

## NAME

gmx-saltbr - Compute salt bridges

## SYNOPSIS

```
gmx saltbr [-f [<.xtc/.trr/...>]] [-s [<.tpr>]] [-b <time>] [-e <time>]
           [-dt <time>] [-t <real>] [-[no]sep]
```

## DESCRIPTION

**gmx saltbr** plots the distance between all combination of charged groups as a function of time. The groups are combined in different ways. A minimum distance can be given (i.e. a cut-off), such that groups that are never closer than that distance will not be plotted.

Output will be in a number of fixed filenames, **min-min.xvg**, **plus-min.xvg** and **plus-plus.xvg**, or files for every individual ion pair if the **-sep** option is selected. In this case, files are named as **sb-(Resname)(Resnr)-(Atomnr)**. There may be **many** such files.

## OPTIONS

Options to specify input files:

- **-f \[\<.xtc/.trr/...\>\] (traj.xtc)**

  Trajectory: *xtc* *trr* *cpt* *gro* *g96* *pdb* *tng*

- **-s \[\<.tpr\>\] (topol.tpr)**

  Portable xdr run input 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)

- **-t \<real\> (1000)**

  Groups that are never closer than this distance are not plotted

- **-\[no\]sep (no)**

  Use separate files for each interaction (may be MANY)

## SEE ALSO

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

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

## COPYRIGHT

2025, GROMACS development team