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# compute event/displace command

## Syntax

    compute ID group-ID event/displace threshold

- ID, group-ID are documented in compute command

- event/displace = style name of this compute command

- threshold = minimum distance any particle must move to trigger an event (distance units)

## Examples

    compute 1 all event/displace 0.5

## Description

Define a computation that flags an “event” if any particle in the group has moved a distance greater than the specified threshold distance when compared to a previously stored reference state (i.e., the previous event). This compute is typically used in conjunction with the prd and tad commands, to detect if a transition to a new minimum energy basin has occurred.

This value calculated by the compute is equal to 0 if no particle has moved far enough, and equal to 1 if one or more particles have moved further than the threshold distance.

Note

If the system is undergoing significant center-of-mass motion, due to thermal motion, an external force, or an initial net momentum, then this compute will not be able to distinguish that motion from local atom displacements and may generate “false positives”.

## Output info

This compute calculates a global scalar (the flag). This value can be used by any command that uses a global scalar value from a compute as input. See the Howto output page for an overview of LAMMPS output options.

The scalar value calculated by this compute is “intensive”. The scalar value will be a 0 or 1 as explained above.

## Restrictions

This command can only be used if LAMMPS was built with the REPLICA package. See the Build package doc page for more info.

## Related commands

prd, tad

## Default

none