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

# gmx-saxs-legacy(1)

Compute small angle X-ray scattering spectra

## NAME

gmx-saxs-legacy - Compute small angle X-ray scattering spectra

## SYNOPSIS

```
gmx saxs-legacy [-f [<.xtc/.trr/...>]] [-s [<.tpr/.gro/...>]]
             [-n [<.ndx>]] [-d [<.dat>]] [-sq [<.xvg>]] [-b <time>]
             [-e <time>] [-dt <time>] [-xvg <enum>] [-ng <int>]
             [-startq <real>] [-endq <real>] [-energy <real>]
```

## DESCRIPTION

**gmx saxs-legacy** calculates SAXS structure factors for given index groups based on Cromer's method. Both topology and trajectory files are required.

## OPTIONS

Options to specify input files:

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

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

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

  Structure+mass(db): *tpr* *gro* *g96* *pdb* brk ent

- **-n \[\<.ndx\>\] (index.ndx) (Optional)**

  Index file

- **-d \[\<.dat\>\] (sfactor.dat) (Optional)**

  Generic data file

Options to specify output files:

- **-sq \[\<.xvg\>\] (sq.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)

- **-xvg \<enum\> (xmgrace)**

  xvg plot formatting: xmgrace, xmgr, none

- **-ng \<int\> (1)**

  Number of groups to compute SAXS

- **-startq \<real\> (0)**

  Starting q (1/nm)

- **-endq \<real\> (60)**

  Ending q (1/nm)

- **-energy \<real\> (12)**

  Energy of the incoming X-ray (keV)

## SEE ALSO

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

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

## COPYRIGHT

2025, GROMACS development team