forked from lijiext/lammps
161 lines
6.9 KiB
Plaintext
161 lines
6.9 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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read_restart command :h3
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[Syntax:]
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read_restart file :pre
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file = name of binary restart file to read in :ul
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[Examples:]
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read_restart save.10000
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read_restart restart.*
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read_restart poly.*.% :pre
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:pre
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[Description:]
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Read in a previously saved simulation from a restart file. This
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allows continuation of a previous run. Information about what is
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stored in a restart file is given below.
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Restart files are saved in binary format to enable exact restarts,
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meaning that the trajectories of a restarted run will precisely match
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those produced by the original run had it continued on.
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Several things can prevent exact restarts due to round-off effects, in
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which case the trajectories in the 2 runs will slowly diverge. These
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include running on a different number of processors or changing
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certain settings such as those set by the "newton"_newton.html or
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"processors"_processors.html commands. LAMMPS will issue a warning in
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these cases.
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Certain fixes will not restart exactly, though they should provide
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statistically similar results. These include "fix
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shake"_fix_shake.html and "fix langevin"_fix_langevin.html.
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Certain pair styles will not restart exactly, though they should
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provide statistically similar results. This is because the forces
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they compute depend on atom velocities, which are used at half-step
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values every timestep when forces are computed. When a run restarts,
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forces are initially evaluated with a full-step velocity, which is
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different than if the run had continued. These pair styles include
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"granular pair styles"_pair_gran.html, "pair dpd"_pair_dpd.html, and
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"pair lubricate"_pair_lubricate.html.
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If a restarted run is immediately different than the run which
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produced the restart file, it could be a LAMMPS bug, so consider
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"reporting it"_Section_errors.html#err_2 if you think the behavior is
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wrong.
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Because restart files are binary, they may not be portable to other
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machines. They can be converted to ASCII data files using the
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"restart2data tool"_Section_tools.html#restart in the tools
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sub-directory of the LAMMPS distribution.
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Similar to how restart files are written (see the
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"write_restart"_write_restart.html and "restart"_restart.html
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commands), the restart filename can contain two wild-card characters.
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If a "*" appears in the filename, the directory is searched for all
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filenames that match the pattern where "*" is replaced with a timestep
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value. The file with the largest timestep value is read in. Thus,
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this effectively means, read the latest restart file. It's useful if
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you want your script to continue a run from where it left off. See
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the "run"_run.html command and its "upto" option for how to specify
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the run command so it doesn't need to be changed either.
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If a "%" character appears in the restart filename, LAMMPS expects a
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set of multiple files to exist. The "restart"_restart.html and
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"write_restart"_write_restart.html commands explain how such sets are
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created. Read_restart will first read a filename where "%" is
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replaced by "base". This file tells LAMMPS how many processors
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created the set. Read_restart then reads the additional files. For
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example, if the restart file was specified as save.% when it was
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written, then read_restart reads the files save.base, save.0, save.1,
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... save.P-1, where P is the number of processors that created the
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restart file. The processors in the current LAMMPS simulation share
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the work of reading these files; each reads a roughly equal subset of
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the files. The number of processors which created the set can be
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different the number of processors in the current LAMMPS simulation.
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This can be a fast mode of input on parallel machines that support
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parallel I/O.
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:line
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A restart file stores the following information about a simulation:
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units and atom style, simulation box size and shape and boundary
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settings, group definitions, per-type atom settings such as mass,
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per-atom attributes including their group assignments and molecular
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topology attributes, force field styles and coefficients, and
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"special_bonds"_special_bonds.html settings. This means that commands
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for these quantities do not need to be re-specified in the input
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script that reads the restart file, though you can redefine settings
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after the restart file is read.
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One exception is that some pair styles do not store their info in
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restart files. The doc pages for individual pair styles note if this
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is the case. This is also true of bond_style hybrid (and angle_style,
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dihedral_style, improper_style hybrid).
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All settings made by the "pair_modify"_pair_modify.html command,
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such as the shift and tail settings, are stored in the restart file
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with the pair style. The one exception is the "pair_modify
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compute"_pair_modify.html setting is not stored.
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Information about "kspace_style"_kspace_style.html settings are not
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stored in the restart file. Hence if you wish to use an Ewald or PPPM
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solver, these commands must be re-issued after the restart file is
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read.
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The list of "fixes"_fix.html used for a simulation is not stored in
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the restart file. This means the new input script should specify all
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fixes it will use. Note that some fixes store an internal "state"
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which is written to the restart file. This allows the fix to continue
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on with its calculations in a restarted simulation. To re-enable such
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a fix, the fix command in the new input script must use the same
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fix-ID and group-ID as was used in the input script that wrote the
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restart file. If a match is found, LAMMPS prints a message indicating
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that the fix is being re-enabled. If no match is found before the
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first run or minimization is performed by the new script, the "state"
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information for the saved fix is discarded. See the doc pages for
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individual fixes for info on which ones can be restarted in this
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manner.
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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 restart file as if they are turned on. This means
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they will need to be turned off again in a new run after the restart
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file is read.
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Bonds that are broken (e.g. by a bond-breaking potential) are written
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to the restart file as broken bonds with a type of 0. Thus these
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bonds will still be broken when the restart file is read.
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IMPORTANT NOTE: No other information is stored in the restart file.
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This means that an input script that reads a restart file should
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specify settings for quantities like "timestep size"_timestep.html,
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"thermodynamic"_thermo_style.html, "neighbor list"_neighbor.html
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criteria including settings made via the
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"neigh_modify"_neigh_modify.html comand, "dump"_dump.html file
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output, "geometric regions"_region.html, etc.
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:line
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[Restrictions:] none
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[Related commands:]
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"read_data"_read_data.html, "read_dump"_read_dump.html,
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"write_restart"_write_restart.html, "restart"_restart.html
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[Default:] none
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