init

doc/src/compute_local_composition_atom.rst

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+.. index:: compute ave/sphere/atom
+.. index:: compute local_composition/atom/kk
+
+compute local_composition/atom command
+================================
+
+Accelerator Variants: *local_composition/atom/kk*
+
+Syntax
+""""""
+
+.. code-block:: LAMMPS
+
+   compute ID group-ID local_composition/atom keyword values ...
+
+* ID, group-ID are documented in :doc:`compute <compute>` command
+* local_composition/atom = style name of this compute command
+* one or more keyword/value pairs may be appended
+
+  .. parsed-literal::
+
+     keyword = *cutoff*
+       *cutoff* value = distance cutoff
+
+Examples
+""""""""
+
+.. code-block:: LAMMPS
+
+   compute 1 all local_composition/atom
+
+   compute 1 all local_composition/atom cutoff 9.0
+   comm_modify cutoff 9.0
+
+..
+   ****** UNDER CONSTRUCTION ******
+   Description
+   """""""""""
+
+   .. versionadded:: 24May2023
+
+   Define a computation that calculates the local composition for each atom based on its neighbors inside a spherical
+   cutoff.  If an atom has :math:`M` neighbors, then its local mass density is
+   calculated as the sum of its mass and its :math:`M` neighbor masses, divided
+   by the volume of the cutoff sphere (or circle in 2d).  The local
+   temperature of the atom is calculated as the temperature of the
+   collection of :math:`M+1` atoms, after subtracting the center-of-mass velocity
+   of the :math:`M+1` atoms from each of the :math:`M+1` atom's velocities.  This
+   is effectively the thermal velocity of the neighborhood of the central
+   atom, similar to :doc:`compute temp/com <compute_temp_com>`.
+
+   The optional keyword *cutoff* defines the distance cutoff used when
+   searching for neighbors. The default value is the cutoff specified by
+   the pair style. If no pair style is defined, then a cutoff must be
+   defined using this keyword. If the specified cutoff is larger than
+   that of the pair_style plus neighbor skin (or no pair style is
+   defined), the *comm_modify cutoff* option must also be set to match
+   that of the *cutoff* keyword.
+
+   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.
+
+   .. note::
+
+      If you have a bonded system, then the settings of
+      :doc:`special_bonds <special_bonds>` command can remove pairwise
+      interactions between atoms in the same bond, angle, or dihedral.
+      This is the default setting for the :doc:`special_bonds
+      <special_bonds>` command, and means those pairwise interactions do
+      not appear in the neighbor list.  Because this compute uses the
+      neighbor list, it also means those pairs will not be included in
+      the order parameter.  This difficulty can be circumvented by
+      writing a dump file, and using the :doc:`rerun <rerun>` command to
+      compute the order parameter for snapshots in the dump file.  The
+      rerun script can use a :doc:`special_bonds <special_bonds>` command
+      that includes all pairs in the neighbor list.
+
+   ----------
+
+
+   .. include:: accel_styles.rst
+
+
+   ----------
+
+   Output info
+   """""""""""
+
+   This compute calculates a per-atom array with two columns: mass
+   density in density :doc:`units <units>` and temperature in temperature
+   :doc:`units <units>`.
+
+   These values can be accessed by any command that uses per-atom values
+   from a compute as input.  See the :doc:`Howto output <Howto_output>`
+   doc page for an overview of LAMMPS output options.
+
+   Restrictions
+   """"""""""""
+
+   This compute is part of the EXTRA-COMPUTE package.  It is only enabled
+   if LAMMPS was built with that package.  See the :doc:`Build package
+   <Build_package>` page for more info.
+
+   Related commands
+   """"""""""""""""
+
+   :doc:`comm_modify <comm_modify>`
+
+   Default
+   """""""
+
+   The option defaults are *cutoff* = pair style cutoff.
+
+..