compute com command — LAMMPS documentation

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# compute com command

## Syntax

    compute ID group-ID com

- ID, group-ID are documented in compute command

- com = style name of this compute command

## Examples

    compute 1 all com

## Description

Define a computation that calculates the center-of-mass of the group of atoms, including all effects due to atoms passing through periodic boundaries.

A vector of three quantities is calculated by this compute, which are the \((x,y,z)\) coordinates of the center of mass.

Note

The coordinates of an atom contribute to the center-of-mass in “unwrapped” form, by using the image flags associated with each atom. See the dump custom command for a discussion of “unwrapped” coordinates. See the Atoms section of the read_data command for a discussion of image flags and how they are set for each atom. You can reset the image flags (e.g., to 0) before invoking this compute by using the set image command.

## Output info

This compute calculates a global vector of length 3, which can be accessed by indices 1–3 by any command that uses global vector values from a compute as input. See the Howto output doc page for an overview of LAMMPS output options.

The vector values are “intensive”. The vector values will be in distance units.

## Restrictions

> none

## Related commands

compute com/chunk

## Default

none