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fix store/force command :h3

[Syntax:]

fix ID group-ID store/force :pre

ID, group-ID are documented in "fix"_fix.html command
store/force = style name of this fix command :ul

[Examples:]

fix 1 all store/force :pre

[Description:]

Store the forces on atoms in the group at the point during each
timestep when the fix is invoked, as described below.  This is useful
for storing forces before constraints or other boundary conditions are
computed which modify the forces, so that unmodified forces can be
"written to a dump file"_dump.html or accessed by other "output
commands"_Section_howto.html#howto_8 that use per-atom quantities.

This fix is invoked at the point in the velocity-Verlet timestepping
immediately after "pair"_pair_style.html, "bond"_bond_style.html
forces have been calculated.  It is the point in the timestep when
various fixes that compute constraint forces are calculated and
potentially modify the force on each atom.  Examples of such fixes are
"fix shake"_fix_shake.html, "fix wall"_fix_wall.html, and "fix
indent"_fix_indent.html.

IMPORTANT NOTE: The order in which various fixes are applied which
operate at the same point during the timestep, is the same as the
order they are specified in the input script.  Thus normally, if you
want to store per-atom forces due to force field interactions, before
constraints are applied, you should list this fix first within that
set of fixes, i.e. before other fixes that apply constraints.
However, if you wish to include certain constraints (e.g. fix shake)
in the stored force, then it could be specified after some fixes and
before others.

[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 produces a per-atom array which can be accessed by various
"output commands"_Section_howto.html#howto_8.  The number of columns
for each atom is 3, and the columns store the x,y,z forces on each
atom.  The per-atom values be accessed on any timestep.

No parameter of this fix can be used with the {start/stop} keywords of
the "run"_run.html command.  This fix is not invoked during "energy
minimization"_minimize.html.

[Restrictions:] none

[Related commands:]

"fix store_state"_fix_store_state.html

[Default:] none
