97 lines
3.1 KiB
Plaintext
97 lines
3.1 KiB
Plaintext
.. index:: fix freeze
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fix freeze command
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==================
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Syntax
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""""""
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.. parsed-literal::
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fix ID group-ID freeze
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* ID, group-ID are documented in :doc:`fix <fix>` command
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* freeze = style name of this fix command
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Examples
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""""""""
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.. parsed-literal::
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fix 2 bottom freeze
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Description
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"""""""""""
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Zero out the force and torque on a granular particle. This is useful
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for preventing certain particles from moving in a simulation. The
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:doc:`granular pair styles <pair_gran>` also detect if this fix has been
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defined and compute interactions between frozen and non-frozen
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particles appropriately, as if the frozen particle has infinite mass.
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A similar functionality for normal (point) particles can be obtained
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using :doc:`fix setforce <fix_setforce>`.
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----------
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Styles with a uffix are functionally the same as the corresponding
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style without the suffix. They have been optimized to run faster,
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depending on your available hardware, as discussed in
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:doc:`Section_accelerate <Section_accelerate>` of the manual. The
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accelerated styles take the same arguments and should produce the same
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results, except for round-off and precision issues.
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These accelerated styles are part of the ackage. They are only
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enabled if LAMMPS was built with that package. See the :ref:`Making LAMMPS <start_3>` section for more info.
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You can specify the accelerated styles explicitly in your input script
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by including their suffix, or you can use the :ref:`-suffix command-line switch <start_7>` when you invoke LAMMPS, or you can
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use the :doc:`suffix <suffix>` command in your input script.
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See :doc:`Section_accelerate <Section_accelerate>` of the manual for
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more instructions on how to use the accelerated styles effectively.
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----------
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Restart, fix_modify, output, run start/stop, minimize info
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""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
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No information about this fix is written to :doc:`binary restart files <restart>`. None of the :doc:`fix_modify <fix_modify>` options
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are relevant to this fix.
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This fix computes a global 3-vector of forces, which can be accessed
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by various :ref:`output commands <howto_15>`. This is the
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total force on the group of atoms before the forces on individual
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atoms are changed by the fix. The vector values calculated by this
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fix are "extensive".
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No parameter of this fix can be used with the *start/stop* keywords of
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the :doc:`run <run>` command. This fix is not invoked during :doc:`energy minimization <minimize>`.
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Restrictions
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""""""""""""
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This fix is part of the GRANULAR package. It is only enabled if
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LAMMPS was built with that package. See the :ref:`Making LAMMPS <start_3>` section for more info.
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There can only be a single freeze fix defined. This is because other
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the :doc:`granular pair styles <pair_gran>` treat frozen particles
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differently and need to be able to reference a single group to which
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this fix is applied.
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Related commands
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""""""""""""""""
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:doc:`atom_style sphere <atom_style>`, :doc:`fix setforce <fix_setforce>`
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**Default:** none
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.. _lws: http://lammps.sandia.gov
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.. _ld: Manual.html
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.. _lc: Section_commands.html#comm
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