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# fix manifoldforce command

## Syntax

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

- ID, group-ID are documented in 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 manifold. This can be used in combination with minimize to remove overlap between particles while keeping them (roughly) constrained to the given manifold, e.g. to set up a run with 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 binary restart files. None of the fix_modify options are relevant to this fix. No global or per-atom quantities are stored by this fix for access by various output commands. No parameter of this fix can be used with the start/stop keywords of the run command. This fix is invoked during energy minimization.

## Restrictions

This fix is part of the MANIFOLD package. It is only enabled if LAMMPS was built with that package. See the Build package 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

fix nve/manifold/rattle, fix nvt/manifold/rattle