# compute basal/atom command

## Syntax

``` LAMMPS
compute ID group-ID basal/atom
```

-   ID, group-ID are documented in [compute](compute) command
-   basal/atom = style name of this compute command

## Examples

``` LAMMPS
compute 1 all basal/atom
```

## Description

Defines a computation that calculates the hexagonal close-packed \"c\"
lattice vector for each atom in the group. It does this by calculating
the normal unit vector to the basal plane for each atom. The results
enable efficient identification and characterization of twins and grains
in hexagonal close-packed structures.

The output of the compute is thus the 3 components of a unit vector
associated with each atom. The components are set to 0.0 for atoms not
in the group.

Details of the calculation are given in [(Barrett)](Barrett).

The neighbor list needed to compute this quantity is constructed each
time the calculation is performed (i.e. each time a snapshot of atoms is
dumped). Thus it can be inefficient to compute/dump this quantity too
frequently or to have multiple compute/dump commands, each of which
computes this quantity.

An example input script that uses this compute is provided in
examples/PACKAGES/basal.

## Output info

This compute calculates a per-atom array with three columns, which can
be accessed by indices 1\--3 by any command that uses per-atom values
from a compute as input. See the [Howto output](Howto_output) doc page
for an overview of LAMMPS output options.

The per-atom vector values are unitless since the three columns
represent components of a unit vector.

## Restrictions

This compute is part of the EXTRA-COMPUTE package. It is only enabled if
LAMMPS was built with that package. See the [Build
package](Build_package) page for more info.

The output of this compute will be meaningless unless the atoms are on
(or near) hcp lattice sites, since the calculation assumes a
well-defined basal plane.

## Related commands

[compute centro/atom](compute_centro_atom), [compute
ackland/atom](compute_ackland_atom)

## Default

none

------------------------------------------------------------------------

::: {#Barrett}
**(Barrett)** Barrett, Tschopp, El Kadiri, Scripta Mat. 66, p.666
(2012).
:::