# write_dump command

## Syntax

``` LAMMPS
write_dump group-ID style file dump-args modify dump_modify-args
```

-   group-ID = ID of the group of atoms to be dumped
-   style = any of the supported [dump styles](dump)
-   file = name of file to write dump info to
-   dump-args = any additional args needed for a particular [dump
    style](dump)
-   modify = all args after this keyword are passed to
    [dump_modify](dump_modify) (optional)
-   dump-modify-args = args for [dump_modify](dump_modify) (optional)

## Examples

``` LAMMPS
write_dump all atom dump.atom
write_dump subgroup atom dump.run.bin
write_dump all custom dump.myforce.* id type x y vx fx
write_dump flow custom dump.%.myforce id type c_myF[3] v_ke modify sort id
write_dump all xyz system.xyz modify sort id element O H
write_dump all image snap*.jpg type type size 960 960 modify backcolor white
write_dump all image snap*.jpg element element &
   bond atom 0.3 shiny 0.1 ssao yes 6345 0.2 size 1600 1600  &
   modify backcolor white element C C O H N C C C O H H S O H
write_dump all atom/gz dump.atom.gz modify compression_level 9
write_dump flow custom/zstd dump.%.myforce.zst &
                id type c_myF[3] v_ke &
                modify sort id &
                compression_level 15
```

## Description

Dump a single snapshot of atom quantities to one or more files for the
current state of the system. This is a one-time immediate operation, in
contrast to the [dump](dump) command which will will set up a dump style
to write out snapshots periodically during a running simulation.

The syntax for this command is mostly identical to that of the
[dump](dump) and [dump_modify](dump_modify) commands as if they were
concatenated together, with the following exceptions: There is no need
for a dump ID or dump frequency and the keyword *modify* is added. The
latter is so that the full range of [dump_modify](dump_modify) options
can be specified for the single snapshot, just as they can be for
multiple snapshots. The *modify* keyword separates the arguments that
would normally be passed to the *dump* command from those that would be
given the *dump_modify*. Both support optional arguments and thus LAMMPS
needs to be able to cleanly separate the two sets of args.

Note that if the specified filename uses wildcard characters \"\*\" or
\"%\", as supported by the [dump](dump) command, they will operate in
the same fashion to create the new filename(s). Normally, [dump
image](dump_image) files require a filename with a \"\*\" character for
the timestep. That is not the case for the write_dump command; no
wildcard \"\*\" character is necessary.

------------------------------------------------------------------------

## Restrictions

All restrictions for the [dump](dump) and [dump_modify](dump_modify)
commands apply to this command as well, with the exception of the [dump
image](dump_image) filename not requiring a wildcard \"\*\" character,
as noted above.

Since dumps are normally written during a [run](run) or [energy
minimization](minimize), the simulation has to be ready to run before
this command can be used. Similarly, if the dump requires information
from a compute, fix, or variable, the information needs to have been
calculated for the current timestep (e.g. by a prior run), else LAMMPS
will generate an error message.

For example, it is not possible to dump per-atom energy with this
command before a run has been performed, since no energies and forces
have yet been calculated. See the [variable](variable) doc page section
on Variable Accuracy for more information on this topic.

## Related commands

[dump](dump), [dump image](dump_image), [dump_modify](dump_modify)

## Default

The defaults are listed on the doc pages for the [dump](dump) and [dump
image](dump_image) and [dump_modify](dump_modify) commands.