"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c

:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Commands_all.html)

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compute ackland/atom command :h3

[Syntax:]

compute ID group-ID ackland/atom keyword/value :pre

ID, group-ID are documented in "compute"_compute.html command :ulb,l
ackland/atom = style name of this compute command :l

zero or more keyword/value pairs may be appended :l
keyword = {legacy} :l
  {legacy} yes/no = use ({yes}) or do not use ({no}) legacy ackland algorithm implementation :pre
:ule

[Examples:]

compute 1 all ackland/atom
compute 1 all ackland/atom legacy yes :pre

[Description:]

Defines a computation that calculates the local lattice structure
according to the formulation given in "(Ackland)"_#Ackland.
Historically, LAMMPS had two, slightly different implementations of
the algorithm from the paper. With the {legacy} keyword, it is
possible to switch between the pre-2015 ({legacy yes}) and post-2015
implementation ({legacy no}). The post-2015 variant is the default.

In contrast to the "centro-symmetry
parameter"_compute_centro_atom.html 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 :ul

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
the "Howto output"_Howto_output.html doc page 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 "Build
package"_Build_package.html doc page for more info.

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

[Related commands:]

"compute centro/atom"_compute_centro_atom.html

[Default:]
The keyword {legacy} defaults to {no}.

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:link(Ackland)
[(Ackland)] Ackland, Jones, Phys Rev B, 73, 054104 (2006).
