92 lines
2.6 KiB
ReStructuredText
92 lines
2.6 KiB
ReStructuredText
.. index:: compute ackland/atom
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compute ackland/atom command
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============================
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Syntax
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""""""
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.. code-block:: LAMMPS
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compute ID group-ID ackland/atom keyword/value
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* ID, group-ID are documented in :doc:`compute <compute>` command
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* ackland/atom = style name of this compute command
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* zero or more keyword/value pairs may be appended
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* keyword = *legacy*
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.. parsed-literal::
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*legacy* args = *yes* or *no* = use (\ *yes*\ ) or do not use (\ *no*\ ) legacy Ackland algorithm implementation
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Examples
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""""""""
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.. code-block:: LAMMPS
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compute 1 all ackland/atom
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compute 1 all ackland/atom legacy yes
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Description
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"""""""""""
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Defines a computation that calculates the local lattice structure
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according to the formulation given in :ref:`(Ackland) <Ackland>`.
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Historically, LAMMPS had two, slightly different implementations of
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the algorithm from the paper. With the *legacy* keyword, it is
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possible to switch between the pre-2015 (\ *legacy yes*\ ) and post-2015
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implementation (\ *legacy no*\ ). The post-2015 variant is the default.
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In contrast to the :doc:`centro-symmetry parameter <compute_centro_atom>` this method is stable against
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temperature boost, because it is based not on the distance between
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particles but the angles. Therefore statistical fluctuations are
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averaged out a little more. A comparison with the Common Neighbor
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Analysis metric is made in the paper.
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The result is a number which is mapped to the following different
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lattice structures:
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* 0 = UNKNOWN
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* 1 = BCC
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* 2 = FCC
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* 3 = HCP
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* 4 = ICO
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The neighbor list needed to compute this quantity is constructed each
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time the calculation is performed (i.e. each time a snapshot of atoms
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is dumped). Thus it can be inefficient to compute/dump this quantity
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too frequently or to have multiple compute/dump commands, each of
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which computes this quantity.-
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Output info
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"""""""""""
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This compute calculates a per-atom vector, which can be accessed by
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any command that uses per-atom values from a compute as input. See
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the :doc:`Howto output <Howto_output>` page for an overview of
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LAMMPS output options.
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Restrictions
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""""""""""""
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This compute is part of the EXTRA-COMPUTE package. It is only enabled if
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LAMMPS was built with that package. See the :doc:`Build package <Build_package>` page for more info.
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The per-atom vector values will be unitless since they are the
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integers defined above.
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Related commands
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""""""""""""""""
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:doc:`compute centro/atom <compute_centro_atom>`
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Default
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"""""""
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The keyword *legacy* defaults to *no*\ .
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----------
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.. _Ackland:
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**(Ackland)** Ackland, Jones, Phys Rev B, 73, 054104 (2006).
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