forked from lijiext/lammps
119 lines
4.8 KiB
Plaintext
119 lines
4.8 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 property/chunk command :h3
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[Syntax:]
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compute ID group-ID property/chunk chunkID input1 input2 ... :pre
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ID, group-ID are documented in "compute"_compute.html command :ulb,l
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property/chunk = style name of this compute command :l
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input = one or more attributes :l
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attributes = count, id, coord1, coord2, coord3
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count = # of atoms in chunk
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id = original chunk IDs before compression by "compute chunk/atom"_compute_chunk_atom.html
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coord123 = coordinates for spatial bins calculated by "compute chunk/atom"_compute_chunk_atom.html :pre
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:ule
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[Examples:]
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compute 1 all property/chunk count
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compute 1 all property/chunk ID coord1 :pre
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[Description:]
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Define a computation that stores the specified attributes of chunks of
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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 and stores the specified attributes of chunks
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as global data so they can be accessed by other "output
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commands"_Section_howto.html#howto_15 and used in conjunction with
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other commands that generate per-chunk data, such as "compute
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com/chunk"_compute_com_chunk.html or "compute
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msd/chunk"_compute_msd_chunk.html.
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Note that only atoms in the specified group contribute to the
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calculation of the {count} attribute. The "compute
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chunk/atom"_compute_chunk_atom.html command defines its own group;
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atoms will have a chunk ID = 0 if they are not in that group,
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signifying they are not assigned to a chunk, and will thus also not
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contribute to this calculation. You can specify the "all" group for
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this command if you simply want to include atoms with non-zero chunk
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IDs.
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The {count} attribute is the number of atoms in the chunk.
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The {id} attribute stores the original chunk ID for each chunk. It
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can only be used if the {compress} keyword was set to {yes} for the
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"compute chunk/atom"_compute_chunk_atom.html command referenced by
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chunkID. This means that the original chunk IDs (e.g. molecule IDs)
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will have been compressed to remove chunk IDs with no atoms assigned
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to them. Thus a compresed chunk ID of 3 may correspond to an original
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chunk ID (molecule ID in this case) of 415. The {id} attribute will
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then be 415 for the 3rd chunk.
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The {coordN} attributes can only be used if a {binning} style was used
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in the "compute chunk/atom"_compute_chunk_atom.html command referenced
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by chunkID. For {bin/1d}, {bin/2d}, and {bin/3d} styles the attribute
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is the center point of the bin in the corresponding dimension. Style
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{bin/1d} only defines a {coord1} attribute. Style {bin/2d} adds a
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{coord2} attribute. Style {bin/3d} adds a {coord3} attribute.
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Note that if the value of the {units} keyword used in the "compute
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chunk/atom command"_compute_chunk_atom.html is {box} or {lattice}, the
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{coordN} attributes will be in distance "units"_units.html. If the
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value of the {units} keyword is {reduced}, the {coordN} attributes
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will be in unitless reduced units (0-1).
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The simplest way to output the results of the compute property/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 myChunk1 all property/chunk cc1
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compute myChunk2 all com/chunk cc1
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fix 1 all ave/time 100 1 100 c_myChunk1 c_myChunk2 file tmp.out mode vector :pre
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[Output info:]
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This compute calculates a global vector or global array depending on
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the number of input values. The length of the vector or number of
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rows in the array is the number of chunks.
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This compute calculates a global vector or global array where the
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number of rows = the number of chunks {Nchunk} as calculated by the
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specified "compute chunk/atom"_compute_chunk_atom.html command. If a
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single input is specified, a global vector is produced. If two or
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more inputs are specified, a global array is produced where the number
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of columns = the number of inputs. The vector or array can be
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accessed by any command that uses global values from a compute as
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input. See "this section"_Section_howto.html#howto_15 for an overview
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of LAMMPS output options.
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The vector or array values are "intensive". The values will be
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unitless or in the units discussed above.
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[Restrictions:] none
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[Related commands:]
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"fix ave/chunk"_fix_ave_chunk.html
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[Default:] none
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