lammps/doc/fix_setforce.txt

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fix setforce command :h3

[Syntax:]

fix ID group-ID setforce fx fy fz :pre

ID, group-ID are documented in "fix"_fix.html command
setforce = style name of this fix command
fx,fy,fz = force component values :ul

[Examples:]

fix freeze indenter setforce 0.0 0.0 0.0
fix 2 edge setforce NULL 0.0 0.0 :pre

[Description:]

Set each component of force on each atom in the group to the specified
values fx,fy,fz.  This erases all previously computed forces on the
atom, though additional fixes could add new forces.  This command can
be used to freeze certain atoms in the simulation by zeroing their
force, assuming their initial velocity zero.

Any of the fx,fy,fz values can be specified as NULL which means do not
alter the force component in that dimension.

[Restart, fix_modify, output, run start/stop, minimize info:]

No information about this fix is written to "binary restart
files"_restart.html.  None of the "fix_modify"_fix_modify.html options
are relevant to this fix.

This fix computes a 3-vector of forces, which can be accessed by
various "output commands"_Section_howto.html#4_15.  This is the total
force on the group of atoms before the forces on individual atoms are
reset by the fix.  The vector values calculated by this fix are
"extensive", meaning they scale with the number of atoms in the
simulation.

No parameter of this fix can be used with the {start/stop} keywords of
the "run"_run.html command.

The forces due to this fix are imposed during an energy minimization,
invoked by the "minimize"_minimize.html command.

[Restrictions:] none

[Related commands:]

"fix addforce"_fix_addforce.html, "fix aveforce"_fix_aveforce.html

[Default:] none