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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2013-04-24 04:53:50 +08:00
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<PRE>write_data file keyword value ...
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2013-04-04 01:06:31 +08:00
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</PRE>
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<UL><LI>file = name of data file to write out
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2013-04-24 04:53:50 +08:00
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<LI>zero or more keyword/value pairs may be appended
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<LI>keyword = <I>pair</I>
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<PRE> <I>pair</I> value = <I>ii</I> or <I>ij</I>
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<I>ii</I> = write one line of pair coefficient info per atom type
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<I>ij</I> = write one line of pair coefficient info per IJ atom type pair
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</PRE>
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2013-04-04 01:06:31 +08:00
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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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2013-04-24 04:53:50 +08:00
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two respects. First, most pair styles do not yet write their
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coefficient information into the data file. This means you will need
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to specify that information in your input script that reads the data
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file, via the <A HREF = "pair_coeff.html">pair_coeff</A> command. Second, a few of
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the <A HREF = "atom_style.html">atom styles</A> (body, ellipsoid, line, tri) that
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store auxiliary "bonus" information about aspherical particles, do not
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yet write the bonus info into the data file. Both these
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functionalities will be added to the write_data command later.
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2013-04-04 01:29:26 +08:00
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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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2013-11-23 01:34:49 +08:00
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using the <A HREF = "Section_start.html#start_7">-r command-line switch</A>.
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2013-04-04 01:29:26 +08:00
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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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2013-04-24 04:53:50 +08:00
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<HR>
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<P>The <I>pair</I> keyword lets you specify in what format the pair
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coefficient information is written into the data file. If the value
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is specified as <I>ii</I>, then one line per atom type is written, to
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specify the coefficients for each of the I=J interactions. This means
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that no cross-interactions for I != J will be specified in the data
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file and the pair style will apply its mixing rule, as documented on
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individual <A HREF = "pair_style.html">pair_style</A> doc pages. Of course this
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behavior can be overridden in the input script after reading the data
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file, by specifying additional <A HREF = "pair_coeff.html">pair_coeff</A> commands
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for any desired I,J pairs.
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</P>
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<P>If the value is specified as <I>ij</I>, then one line of coefficients is
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written for all I,J pairs where I <= J. These coefficients will
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include any specific settings made in the input script up to that
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point. The presence of these I != J coefficients in the data file
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will effectively turn off the default mixing rule for the pair style.
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Again, the coefficient values in the data file can can be overridden
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in the input script after reading the data file, by specifying
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additional <A HREF = "pair_coeff.html">pair_coeff</A> commands for any desired I,J
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pairs.
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</P>
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<HR>
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2013-04-04 01:06:31 +08:00
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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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2013-04-24 04:53:50 +08:00
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<P><B>Default:</B>
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</P>
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<P>The option defaults are pair = ii.
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2013-04-04 01:06:31 +08:00
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</P>
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</HTML>
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