58 lines
2.2 KiB
ReStructuredText
58 lines
2.2 KiB
ReStructuredText
LAMMPS input scripts
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====================
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LAMMPS executes by reading commands from a input script (text file),
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one line at a time. When the input script ends, LAMMPS exits. Each
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command causes LAMMPS to take some action. It may set an internal
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variable, read in a file, or run a simulation. Most commands have
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default settings, which means you only need to use the command if you
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wish to change the default.
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In many cases, the ordering of commands in an input script is not
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important. However the following rules apply:
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(1) LAMMPS does not read your entire input script and then perform a
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simulation with all the settings. Rather, the input script is read
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one line at a time and each command takes effect when it is read.
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Thus this sequence of commands:
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.. code-block:: LAMMPS
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timestep 0.5
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run 100
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run 100
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does something different than this sequence:
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.. code-block:: LAMMPS
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run 100
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timestep 0.5
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run 100
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In the first case, the specified timestep (0.5 fs) is used for two
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simulations of 100 timesteps each. In the 2nd case, the default
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timestep (1.0 fs) is used for the 1st 100 step simulation and a 0.5 fs
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timestep is used for the 2nd one.
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(2) Some commands are only valid when they follow other commands. For
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example you cannot set the temperature of a group of atoms until atoms
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have been defined and a group command is used to define which atoms
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belong to the group.
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(3) Sometimes command B will use values that can be set by command A.
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This means command A must precede command B in the input script if it
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is to have the desired effect. For example, the
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:doc:`read\_data <read_data>` command initializes the system by setting
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up the simulation box and assigning atoms to processors. If default
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values are not desired, the :doc:`processors <processors>` and
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:doc:`boundary <boundary>` commands need to be used before read\_data to
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tell LAMMPS how to map processors to the simulation box.
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Many input script errors are detected by LAMMPS and an ERROR or
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WARNING message is printed. The :doc:`Errors <Errors>` doc page gives
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more information on what errors mean. The documentation for each
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command lists restrictions on how the command can be used.
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