fix nve/noforce command — LAMMPS documentation

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# fix nve/noforce command

## Syntax

    fix ID group-ID nve

- ID, group-ID are documented in fix command

- nve/noforce = style name of this fix command

## Examples

    fix 3 wall nve/noforce

## Description

Perform updates of position, but not velocity for atoms in the group each timestep. In other words, the force on the atoms is ignored and their velocity is not updated. The atom velocities are used to update their positions.

This can be useful for wall atoms, when you set their velocities, and want the wall to move (or stay stationary) in a prescribed fashion.

This can also be accomplished via the fix setforce command, but with fix nve/noforce, the forces on the wall atoms are unchanged, and can thus be printed by the dump command or queried with an equal-style variable that uses the fcm() group function to compute the total force on the group of atoms.

## 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 not invoked during energy minimization.

## Restrictions

none

## Related commands

fix nve

## Default

none