"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c

:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Section_commands.html#comm)

:line

write_data command :h3

[Syntax:]

write_data file :pre

file = name of data file to write out :ul

[Examples:]

write_data data.polymer
write_data data.* :pre

[Description:]

Write a data file in text format of the current state of the
simulation.  Data files can be read by the "read data"_read_data.html
command to begin a simulation.  The "read_data"_read_data.html command
also describes their format.

Similar to "dump"_dump.html files, the data filename can contain a "*"
wild-card character.  The "*" is replaced with the current timestep
value.

IMPORTANT NOTE: The write-data command is not yet fully implemented in
two respects.  First, most pair, bond, angle, dihedral, improper
styles do not yet write their coefficient information into the data
file.  This means you will need to specify that information in your
input script that reads the data file, e.g. with the
"pair_coeff"_pair_coeff.html command.  Second, a few of the "atom
styles"_atom_style.html (body, ellipsoid, line, tri) that store
auxiliary "bonus" information about aspherical particles, do not yet
write the bonus info into the data file.  Both these functionalities
will be added to the write_data command later.

Because a data file is in text format, if you use a data file written
out by this command to restart a simulation, the initial state of the
new run will be slightly different than the final state of the old run
(when the file was written) which was represented internally by LAMMPS
in binary format.  A new simulation which reads the data file will
thus typically diverge from a simulation that continued in the
original input script.

If you want to do more exact restarts, using binary files, see the
"restart"_restart.html, "write_restart"_write_restart.html, and
"read_restart"_read_restart.html commands.  You can also convert
binary restart files to text data files, after a simulation has run,
using the "restart2data"_Section_tools.html#restart2data tool in the
tools directory.  When the write_data command is fully implemented
(see NOTE above), the restart2data command will be obsolete and will
be removed from the LAMMPS distribution.

IMPORTANT NOTE: Only limited information about a simulation is stored
in a data file.  For example, no information about atom
"groups"_group.html and "fixes"_fix.html are stored.  "Binary restart
files"_read_restart.html store more information.

Bond interactions (angle, etc) that have been turned off by the "fix
shake"_fix_shake.html or "delete_bonds"_delete_bonds.html command will
be written to a data file as if they are turned on.  This means they
will need to be turned off again in a new run after the data file is
read.

Bonds that are broken (e.g. by a bond-breaking potential) are not
written to the data file.  Thus these bonds will not exist when the
data file is read.

[Restrictions:]

This command requires inter-processor communication to migrate atoms
before the data file is written.  This means that your system must be
ready to perform a simulation before using this command (force fields
setup, atom masses initialized, etc).

[Related commands:]

"read_data"_read_data.html, "write_restart"_write_restart.html

[Default:] none
