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
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:link(lws,http://lammps.sandia.gov)
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:link(ld,Manual.html)
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:link(lc,Section_commands.html#comm)
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:line
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compute angmom/chunk command :h3
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[Syntax:]
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compute ID group-ID angmom/chunk chunkID :pre
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ID, group-ID are documented in "compute"_compute.html command
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angmom/chunk = style name of this compute command
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chunkID = ID of "compute chunk/atom"_compute_chunk_atom.html command :ul
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[Examples:]
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compute 1 fluid angmom/chunk molchunk :pre
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[Description:]
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Define a computation that calculates the angular momemtum of multiple
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chunks of atoms.
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In LAMMPS, chunks are collections of atoms defined by a "compute
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chunk/atom"_compute_chunk_atom.html command, which assigns each atom
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to a single chunk (or no chunk). The ID for this command is specified
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as chunkID. For example, a single chunk could be the atoms in a
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molecule or atoms in a spatial bin. See the "compute
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chunk/atom"_compute_chunk_atom.html doc page and ""Section_howto
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23"_Section_howto.html#howto_23 for details of how chunks can be
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defined and examples of how they can be used to measure properties of
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a system.
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This compute calculates the 3 components of the angular momentum
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vector for each chunk, due to the velocity/momentum of the individual
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atoms in the chunk around the center-of-mass of the chunk. The
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calculation includes all effects due to atoms passing thru periodic
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boundaries.
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Note that only atoms in the specified group contribute to the
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calculation. The "compute chunk/atom"_compute_chunk_atom.html command
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defines its own group; atoms will have a chunk ID = 0 if they are not
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in that group, signifying they are not assigned to a chunk, and will
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thus also not contribute to this calculation. You can specify the
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"all" group for this command if you simply want to include atoms with
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non-zero chunk IDs.
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IMPORTANT NOTE: The coordinates of an atom contribute to the chunk's
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angular momentum in "unwrapped" form, by using the image flags
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associated with each atom. See the "dump custom"_dump.html command
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for a discussion of "unwrapped" coordinates. See the Atoms section of
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the "read_data"_read_data.html command for a discussion of image flags
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and how they are set for each atom. You can reset the image flags
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(e.g. to 0) before invoking this compute by using the "set
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image"_set.html command.
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The simplest way to output the results of the compute angmom/chunk
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calculation to a file is to use the "fix ave/time"_fix_ave_time.html
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command, for example:
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compute cc1 all chunk/atom molecule
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compute myChunk all angmom/chunk cc1
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fix 1 all ave/time 100 1 100 c_myChunk file tmp.out mode vector :pre
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[Output info:]
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This compute calculates a global array where the number of rows = the
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number of chunks {Nchunk} as calculated by the specified "compute
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chunk/atom"_compute_chunk_atom.html command. The number of columns =
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3 for the 3 xyz components of the angular momentum for each chunk.
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These values can be accessed by any command that uses global array
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values from a compute as input. See "Section_howto
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15"_Section_howto.html#howto_15 for an overview of LAMMPS output
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options.
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The array values are "intensive". The array values will be in
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mass-velocity-distance "units"_units.html.
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[Restrictions:] none
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[Related commands:]
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"variable angmom() function"_variable.html
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[Default:] none
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