# fix qmmm command

## Syntax

    fix ID group-ID qmmm

-   ID, group-ID are documented in [fix](fix) command
-   qmmm = style name of this fix command

## Examples

``` LAMMPS
fix 1 qmol qmmm
```

## Description

This fix provides functionality to enable a quantum mechanics/molecular
mechanics (QM/MM) coupling of LAMMPS to a quantum mechanical code. The
current implementation only supports an ONIOM style mechanical coupling
to the [Quantum ESPRESSO](https://www.quantum-espresso.org)\_ plane wave
DFT package. Electrostatic coupling is in preparation and the interface
has been written in a manner that coupling to other QM codes should be
possible without changes to LAMMPS itself.

The interface code for this is in the lib/qmmm directory of the LAMMPS
distribution and is being made available at this early stage of
development in order to encourage contributions for interfaces to other
QM codes. This will allow the LAMMPS side of the implementation to be
adapted if necessary before being finalized.

Details about how to use this fix are currently documented in the
description of the QM/MM interface code itself in lib/qmmm/README.

## Restart, fix_modify, output, run start/stop, minimize info

No information about this fix is written to [binary restart
files](restart). None of the [fix_modify](fix_modify) options are
relevant to this fix. No global scalar or vector or per-atom quantities
are stored by this fix for access by various [output
commands](Howto_output). No parameter of this fix can be used with the
*start/stop* keywords of the [run](run) command. This fix is not invoked
during [energy minimization](minimize).

## Restrictions

This fix is part of the QMMM package. It is only enabled if LAMMPS was
built with that package. It also requires building a library provided
with LAMMPS. See the [Build package](Build_package) page for more info.

The fix is only functional when LAMMPS is built as a library and linked
with a compatible QM program and a QM/MM front end into a QM/MM
executable. See the lib/qmmm/README file for details.

## Related commands

none

## Default

none