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### fix addforce command

Syntax:

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

- ID, group-ID are documented in fix command
- addforce = 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 kick flow addforce 1.0 0.0 0.0

Description:

Add fx,fy,fz to the corresponding component of force for each atom in the group. This command can be used to give an additional push to atoms in a simulation, such as for a simulation of Poiseuille flow in a channel.

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.

The fix_modify energy option is supported by this fix to add the potential "energy" inferred by the added force to the system's potential energy as part of thermodynamic output. This is a fictitious quantity but is needed so that the minimize command can include the forces added by this fix in a consistent manner. I.e. there is a decrease in potential energy when atoms move in the direction of the added force.

This fix computes a scalar and a 3-vector of forces, which can be accessed by various output commands. The scalar is the potential energy discussed above. The vector is the total force on the group of atoms before the forces on individual atoms are changed by the fix. The scalar 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.

IMPORTANT NOTE: If you want the fictitious potential energy associated with the added forces to be included in the total potential energy of the system (the quantity being minimized), you MUST enable the fix_modify energy option for this fix.

Restrictions: none

Related commands:

fix setforce, fix aveforce

Default: none