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### fix aveforce command

Syntax:

    fix ID group-ID aveforce fx fy fz keyword value ...

- ID, group-ID are documented in fix command
- aveforce = style name of this fix command
- fx,fy,fz = force component values (force units)
- zero or more keyword/value pairs may be appended to args
- keyword = region

        region value = region-ID
          region-ID = ID of region atoms must be in to have added force

Examples:

    fix pressdown topwall aveforce 0.0 -1.0 0.0
    fix 2 bottomwall aveforce NULL -1.0 0.0 region top

Description:

Apply an additional external force to a group of atoms in such a way that every atom experiences the same force. This is useful for pushing on wall or boundary atoms so that the structure of the wall does not change over time.

The existing force is averaged for the group of atoms, component by component. The actual force on each atom is then set to the average value plus the component specified in this command. This means each atom in the group receives the same force.

If any of the arguments is specified as NULL then the forces in that dimension are not changed. Note that this is not the same as specifying a 0.0 value, since that sets all forces to the same average value without adding in any additional force.

If the region keyword is used, the atom must also be in the specified geometric region in order to have force added to it.

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.

This fix computes a 3-vector of forces, which can be accessed by various output commands. This is the total force on the group of atoms before the forces on individual atoms are changed by the fix. The vector values calculated by this fix are "extensive".

No parameter of this fix can be used with the start/stop keywords of the run command.

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

Restrictions: none

Related commands:

fix setforce, fix addforce

Default: none