2013-04-04 01:06:31 +08:00
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<CENTER><A HREF = "http://lammps.sandia.gov">LAMMPS WWW Site</A> - <A HREF = "Manual.html">LAMMPS Documentation</A> - <A HREF = "Section_commands.html#comm">LAMMPS Commands</A>
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<HR>
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<H3>write_data command
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</H3>
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<P><B>Syntax:</B>
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</P>
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<PRE>write_data file
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</PRE>
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<UL><LI>file = name of data file to write out
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</UL>
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<P><B>Examples:</B>
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</P>
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2013-04-04 01:29:26 +08:00
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<PRE>write_data data.polymer
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write_data data.*
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2013-04-04 01:06:31 +08:00
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</PRE>
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<P><B>Description:</B>
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</P>
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2013-04-04 01:29:26 +08:00
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<P>Write a data file in text format of the current state of the
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simulation. Data files can be read by the <A HREF = "read_data.html">read data</A>
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command to begin a simulation. The <A HREF = "read_data.html">read_data</A> command
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also describes their format.
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</P>
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<P>Similar to <A HREF = "dump.html">dump</A> files, the data filename can contain a "*"
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wild-card character. The "*" is replaced with the current timestep
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value.
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</P>
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<P>IMPORTANT NOTE: The write-data command is not yet fully implemented in
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two respects. First, most pair, bond, angle, dihedral, improper
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styles do not yet write their coefficient information into the data
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file. This means you will need to specify that information in your
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input script that reads the data file, e.g. with the
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<A HREF = "pair_coeff.html">pair_coeff</A> command. Second, a few of the <A HREF = "atom_style.html">atom
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styles</A> (body, ellipsoid, line, tri) that store
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auxiliary "bonus" information about aspherical particles, do not yet
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write the bonus info into the data file. Both these functionalities
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will be added to the write_data command later.
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</P>
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<P>Because a data file is in text format, if you use a data file written
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out by this command to restart a simulation, the initial state of the
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new run will be slightly different than the final state of the old run
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(when the file was written) which was represented internally by LAMMPS
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in binary format. A new simulation which reads the data file will
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thus typically diverge from a simulation that continued in the
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original input script.
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</P>
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<P>If you want to do more exact restarts, using binary files, see the
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<A HREF = "restart.html">restart</A>, <A HREF = "write_restart.html">write_restart</A>, and
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<A HREF = "read_restart.html">read_restart</A> commands. You can also convert
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binary restart files to text data files, after a simulation has run,
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using the <A HREF = "Section_tools.html#restart2data">restart2data</A> tool in the
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tools directory. When the write_data command is fully implemented
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(see NOTE above), the restart2data command will be obsolete and will
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be removed from the LAMMPS distribution.
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</P>
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<P>IMPORTANT NOTE: Only limited information about a simulation is stored
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in a data file. For example, no information about atom
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<A HREF = "group.html">groups</A> and <A HREF = "fix.html">fixes</A> are stored. <A HREF = "read_restart.html">Binary restart
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files</A> store more information.
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</P>
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<P>Bond interactions (angle, etc) that have been turned off by the <A HREF = "fix_shake.html">fix
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shake</A> or <A HREF = "delete_bonds.html">delete_bonds</A> command will
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be written to a data file as if they are turned on. This means they
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will need to be turned off again in a new run after the data file is
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read.
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</P>
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<P>Bonds that are broken (e.g. by a bond-breaking potential) are not
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written to the data file. Thus these bonds will not exist when the
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data file is read.
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2013-04-04 01:06:31 +08:00
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</P>
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<P><B>Restrictions:</B>
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</P>
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<P>This command requires inter-processor communication to migrate atoms
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before the data file is written. This means that your system must be
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ready to perform a simulation before using this command (force fields
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setup, atom masses initialized, etc).
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</P>
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<P><B>Related commands:</B>
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</P>
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<P><A HREF = "read_data.html">read_data</A>, <A HREF = "write_restart.html">write_restart</A>
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</P>
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<P><B>Default:</B> none
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</P>
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</HTML>
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