# compute event/displace command

## Syntax

``` LAMMPS
compute ID group-ID event/displace threshold
```

-   ID, group-ID are documented in [compute](compute) command
-   event/displace = style name of this compute command
-   threshold = minimum distance any particle must move to trigger an
    event (distance units)

## Examples

``` LAMMPS
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](prd) and [tad](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
::: title
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](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](Build_package) doc page for more info.

## Related commands

[prd](prd), [tad](tad)

## Default

none