.. index:: fix manifoldforce

fix manifoldforce command
=========================

Syntax
""""""


.. parsed-literal::

   fix ID group-ID manifoldforce manifold manifold-args ...

* ID, group-ID are documented in :doc:`fix <fix>` command
* manifold = name of the manifold
* manifold-args = parameters for the manifold


Examples
""""""""

fix constrain all manifoldforce sphere 5.0

Description
"""""""""""

This fix subtracts each time step from the force the component along
the normal of the specified :doc:`manifold <Howto_manifold>`.  This can be
used in combination with :doc:`minimize <minimize>` to remove overlap
between particles while keeping them (roughly) constrained to the
given manifold, e.g. to set up a run with :doc:`fix nve/manifold/rattle <fix_nve_manifold_rattle>`.  I have found that
only *hftn* and *quickmin* with a very small time step perform
adequately though.


----------


**Restart, fix\_modify, output, run start/stop, minimize info:**

No information about this fix is written to :doc:`binary restart files <restart>`.  None of the :doc:`fix\_modify <fix_modify>` options
are relevant to this fix.  No global or per-atom quantities are stored
by this fix for access by various :doc:`output commands <Howto_output>`.
No parameter of this fix can be used with the *start/stop* keywords of
the :doc:`run <run>` command.  This fix is invoked during :doc:`energy minimization <minimize>`.


----------


Restrictions
""""""""""""


This fix is part of the USER-MANIFOLD package. It is only enabled if
LAMMPS was built with that package.  See the :doc:`Build package <Build_package>` doc page for more info.

Only use this with *min\_style hftn* or *min\_style quickmin*. If not,
the constraints will not be satisfied very well at all. A warning is
generated if the *min\_style* is incompatible but no error.


----------


Related commands
""""""""""""""""

:doc:`fix nve/manifold/rattle <fix_nve_manifold_rattle>`, :doc:`fix nvt/manifold/rattle <fix_nvt_manifold_rattle>`


.. _lws: http://lammps.sandia.gov
.. _ld: Manual.html
.. _lc: Commands_all.html
