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### compute basal/atom command

Syntax:

    compute ID group-ID basal/atom

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

Examples:

    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 associdate with each atom. The components are set to 0.0 for atoms not in the group.

Details of the calculation are given in (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/USER/misc/basal.

Output info:

This compute calculates a per-atom array with 3 columns, which can be accessed by indices 1-3 by any command that uses per-atom values from a compute as input. See Section_howto 15 for an overview of LAMMPS output options.

The per-atom vector values are unitless since the 3 columns represent components of a unit vector.

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 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 ackland/atom

Default: none

(Barrett) Barrett, Tschopp, El Kadiri, Scripta Mat. 66, p.666 (2012).