forked from lijiext/lammps
90 lines
3.3 KiB
Plaintext
90 lines
3.3 KiB
Plaintext
"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 omega/chunk command :h3
|
|
|
|
[Syntax:]
|
|
|
|
compute ID group-ID omega/chunk chunkID :pre
|
|
|
|
ID, group-ID are documented in "compute"_compute.html command
|
|
omega/molecule = style name of this compute command
|
|
chunkID = ID of "compute chunk/atom"_compute_chunk_atom.html command :ul
|
|
|
|
[Examples:]
|
|
|
|
compute 1 fluid omega/chunk molchunk :pre
|
|
|
|
[Description:]
|
|
|
|
Define a computation that calculates the angular velocity (omega) of
|
|
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 angular velocity
|
|
vector for each chunk, via the formula L = Iw where L is the angular
|
|
momentum vector of the chunk, I is its moment of inertia tensor, and w
|
|
is omega = angular velocity 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
|
|
angular velocity 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 omega/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 omega/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 angular velocity 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
|
|
velocity/distance "units"_units.html.
|
|
|
|
[Restrictions:] none
|
|
|
|
[Related commands:]
|
|
|
|
"variable omega() function"_variable.html
|
|
|
|
[Default:] none
|