forked from lijiext/lammps
121 lines
4.7 KiB
Plaintext
121 lines
4.7 KiB
Plaintext
"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c
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:link(lws,http://lammps.sandia.gov)
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:link(ld,Manual.html)
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:link(lc,Section_commands.html#comm)
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:line
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write_data command :h3
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[Syntax:]
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write_data file keyword value ... :pre
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file = name of data file to write out :ulb,l
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zero or more keyword/value pairs may be appended :l
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keyword = {pair} :l
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{pair} value = {ii} or {ij}
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{ii} = write one line of pair coefficient info per atom type
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{ij} = write one line of pair coefficient info per IJ atom type pair :pre
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:ule
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[Examples:]
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write_data data.polymer
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write_data data.* :pre
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[Description:]
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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 "read data"_read_data.html
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command to begin a simulation. The "read_data"_read_data.html command
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also describes their format.
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Similar to "dump"_dump.html 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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IMPORTANT NOTE: The write-data command is not yet fully implemented in
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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 "pair_coeff"_pair_coeff.html command. Second, a few of
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the "atom styles"_atom_style.html (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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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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If you want to do more exact restarts, using binary files, see the
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"restart"_restart.html, "write_restart"_write_restart.html, and
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"read_restart"_read_restart.html 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 "restart2data"_Section_tools.html#restart2data 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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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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"groups"_group.html and "fixes"_fix.html are stored. "Binary restart
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files"_read_restart.html store more information.
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Bond interactions (angle, etc) that have been turned off by the "fix
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shake"_fix_shake.html or "delete_bonds"_delete_bonds.html 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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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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:line
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The {pair} 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 {ii}, 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 "pair_style"_pair_style.html 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 "pair_coeff"_pair_coeff.html commands
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for any desired I,J pairs.
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If the value is specified as {ij}, 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 "pair_coeff"_pair_coeff.html commands for any desired I,J
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pairs.
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:line
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[Restrictions:]
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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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[Related commands:]
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"read_data"_read_data.html, "write_restart"_write_restart.html
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[Default:]
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The option defaults are pair = ii.
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