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

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

:line

compute torque/chunk command :h3

[Syntax:]

compute ID group-ID torque/chunk chunkID :pre

ID, group-ID are documented in "compute"_compute.html command
torque/chunk = style name of this compute command
chunkID = ID of "compute chunk/atom"_compute_chunk_atom.html command :ul

[Examples:]

compute 1 fluid torque/chunk molchunk :pre

[Description:]

Define a computation that calculates the torque on multiple chunks of
atoms.

In LAMMPS, chunks are collections of atoms defined by a "compute
chunk/atom"_compute_chunk_atom.html command, which assigns each atom
to a single chunk (or no chunk).  The ID for this command is specified
as chunkID.  For example, a single chunk could be the atoms in a
molecule or atoms in a spatial bin.  See the "compute
chunk/atom"_compute_chunk_atom.html doc page and ""Section_howto
23"_Section_howto.html#howto_23 for details of how chunks can be
defined and examples of how they can be used to measure properties of
a system.

This compute calculates the 3 components of the torque vector for eqch
chunk, due to the forces on the individual atoms in the chunk around
the center-of-mass of the chunk.  The calculation includes all effects
due to atoms passing thru periodic boundaries.

Note that only atoms in the specified group contribute to the
calculation.  The "compute chunk/atom"_compute_chunk_atom.html command
defines its own group; atoms will have a chunk ID = 0 if they are not
in that group, signifying they are not assigned to a chunk, and will
thus also not contribute to this calculation.  You can specify the
"all" group for this command if you simply want to include atoms with
non-zero chunk IDs.

IMPORTANT NOTE: The coordinates of an atom contribute to the chunk's
torque in "unwrapped" form, by using the image flags associated with
each atom.  See the "dump custom"_dump.html command for a discussion
of "unwrapped" coordinates.  See the Atoms section of the
"read_data"_read_data.html command for a discussion of image flags and
how they are set for each atom.  You can reset the image flags
(e.g. to 0) before invoking this compute by using the "set
image"_set.html command.

The simplest way to output the results of the compute torque/chunk
calculation to a file is to use the "fix ave/time"_fix_ave_time.html
command, for example:

compute cc1 all chunk/atom molecule
compute myChunk all torque/chunk cc1
fix 1 all ave/time 100 1 100 c_myChunk file tmp.out mode vector :pre

[Output info:]

This compute calculates a global array where the number of rows = the
number of chunks {Nchunk} as calculated by the specified "compute
chunk/atom"_compute_chunk_atom.html command.  The number of columns =
3 for the 3 xyz components of the torque for each chunk.  These values
can be accessed by any command that uses global array values from a
compute as input.  See "Section_howto 15"_Section_howto.html#howto_15
for an overview of LAMMPS output options.

The array values are "intensive".  The array values will be in
force-distance "units"_units.html.

[Restrictions:] none

[Related commands:]

"variable torque() function"_variable.html

[Default:] none
