# compute ackland/atom command

## Syntax

compute ID group-ID ackland/atom

• ID, group-ID are documented in compute command
• ackland/atom = style name of this compute command

## Examples

compute 1 all ackland/atom


## Description

Defines a computation that calculates the local lattice structure according to the formulation given in (Ackland).

In contrast to the centro-symmetry parameter this method is stable against temperature boost, because it is based not on the distance between particles but the angles. Therefore statistical fluctuations are averaged out a little more. A comparison with the Common Neighbor Analysis metric is made in the paper.

The result is a number which is mapped to the following different lattice structures:

• 0 = UNKNOWN
• 1 = BCC
• 2 = FCC
• 3 = HCP
• 4 = ICO

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.-

Output info:

This compute calculates a per-atom vector, which can be accessed by any command that uses per-atom values from a compute as input. See Section 6.15 for an overview of LAMMPS output options.

## Restrictions

This compute is part of the USER-MISC package. It is only enabled if LAMMPS was built with that package. See the Making LAMMPS section for more info.

The per-atom vector values will be unitless since they are the integers defined above.