group2ndx command — LAMMPS 15 May 2015 version documentation

# group2ndx command

## Syntax

    group2ndx file group-ID ...

- file = name of index file to write out
- zero or more group IDs may be appended

## Examples

    group2ndx allindex.ndx
    group2ndx someindex.ndx upper lower mobile

## Description

Write a Gromacs style index file in text format that associates atom IDs with the corresponding group definitions. This index file can be used with in combination with Gromacs analysis tools or to import group definitions into the fix colvars input file.

Without specifying any group IDs, all groups will be written to the index file. When specifying group IDs, only those groups will be written to the index file. In order to follow the Gromacs conventions, the group all will be renamed to System in the index file.

## Restrictions

This command requires that atoms have atom IDs, since this is the information that is written to the index file.

This fix is part of the USER-COLVARS package. It is only enabled if LAMMPS was built with that package. See the Making LAMMPS section for more info.

## Related commands

group, dump, fix colvars

Default: none