\(\renewcommand{\AA}{\text{Å}}\)

# compute contact/atom command

## Syntax

    compute ID group-ID contact/atom group2-ID

- ID, group-ID are documented in compute command

- contact/atom = style name of this compute command

- group2-ID = optional argument to restrict which atoms to consider for contacts (see below)

## Examples

    compute 1 all contact/atom
    compute 1 all contact/atom mygroup

## Description

Define a computation that calculates the number of contacts for each atom in a group.

The contact number is defined for finite-size spherical particles as the number of neighbor atoms which overlap the central particle, meaning that their distance of separation is less than or equal to the sum of the radii of the two particles.

The value of the contact number will be 0.0 for atoms not in the specified compute group.

The optional group2-ID argument allows to specify from which group atoms contribute to the coordination number. Default setting is group ‘all’.

## Output info

This compute calculates a per-atom vector, whose values can be accessed by any command that uses per-atom values from a compute as input. See the Howto output page for an overview of LAMMPS output options.

The per-atom vector values will be a number \(\ge 0.0\), as explained above.

## Restrictions

This compute is part of the GRANULAR package. It is only enabled if LAMMPS was built with that package. See the Build package page for more info.

This compute requires that atoms store a radius as defined by the atom_style sphere command.

## Related commands

compute coord/atom

## Default

group2-ID = all