forked from lijiext/lammps
118 lines
4.8 KiB
Plaintext
118 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 pair/local command :h3
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[Syntax:]
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compute ID group-ID pair/local input1 input2 ... :pre
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ID, group-ID are documented in "compute"_compute.html command :ulb,l
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pair/local = style name of this compute command :l
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zero or more keywords may be appended :l
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keyword = {dist} or {eng} or {force} or {fx} or {fy} or {fz} or {pN} :l
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{dist} = pairwise distance
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{eng} = pairwise energy
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{force} = pairwise force
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{fx},{fy},{fz} = components of pairwise force
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{pN} = pair style specific quantities for allowed N values :pre
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:ule
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[Examples:]
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compute 1 all pair/local eng
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compute 1 all pair/local dist eng force
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compute 1 all pair/local dist eng fx fy fz
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compute 1 all pair/local dist fx fy fz p1 p2 p3 :pre
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[Description:]
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Define a computation that calculates properties of individual pairwise
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interactions. The number of datums generated, aggregated across all
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processors, equals the number of pairwise interactions in the system.
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The local data stored by this command is generated by looping over the
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pairwise neighbor list. Info about an individual pairwise interaction
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will only be included if both atoms in the pair are in the specified
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compute group, and if the current pairwise distance is less than the
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force cutoff distance for that interaction, as defined by the
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"pair_style"_pair_style.html and "pair_coeff"_pair_coeff.html
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commands.
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The output {dist} is the distance bewteen the pair of atoms.
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The output {eng} is the interaction energy for the pair of atoms.
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The output {force} is the force acting between the pair of atoms,
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which is positive for a repulsive force and negative for an attractive
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force. The outputs {fx}, {fy}, and {fz} are the xyz components of
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{force} on atom I.
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A pair style may define additional pairwise quantities which can be
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accessed as {p1} to {pN}, where N is defined by the pair style. Most
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pair styles do not define any additional quantities, so N = 0. An
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example of ones that do are the "granular pair styles"_pair_gran.html
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which calculate the tangential force between two particles and return
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its components and magnitude acting on atom I for N = 1,2,3,4. See
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individual pair styles for detils.
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The output {dist} will be in distance "units"_units.html. The output
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{eng} will be in energy "units"_units.html. The outputs {force},
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{fx}, {fy}, and {fz} will be in force "units"_units.html. The output
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{pN} will be in whatever units the pair style defines.
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Note that as atoms migrate from processor to processor, there will be
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no consistent ordering of the entries within the local vector or array
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from one timestep to the next. The only consistency that is
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guaranteed is that the ordering on a particular timestep will be the
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same for local vectors or arrays generated by other compute commands.
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For example, pair output from the "compute
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property/local"_compute_property_local.html command can be combined
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with data from this command and output by the "dump local"_dump.html
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command in a consistent way.
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NOTE: For pairs, if two atoms I,J are involved in 1-2, 1-3, 1-4
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interactions within the molecular topology, their pairwise interaction
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may be turned off, and thus they may not appear in the neighbor list,
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and will not be part of the local data created by this command. More
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specifically, this will be true of I,J pairs with a weighting factor
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of 0.0; pairs with a non-zero weighting factor are included. The
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weighting factors for 1-2, 1-3, and 1-4 pairwise interactions are set
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by the "special_bonds"_special_bonds.html command. An exception is if
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long-range Coulombics are being computed via the
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"kspace_style"_kspace_style.html command, then atom pairs with
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weighting factors of zero are still included in the neighbor list, so
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that a portion of the long-range interaction contribution can be
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computed in the pair style. Hence in that case, those atom pairs will
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be part of the local data created by this command.
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[Output info:]
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This compute calculates a local vector or local array depending on the
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number of keywords. The length of the vector or number of rows in the
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array is the number of pairs. If a single keyword is specified, a
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local vector is produced. If two or more keywords are specified, a
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local array is produced where the number of columns = the number of
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keywords. The vector or array can be accessed by any command that
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uses local values from a compute as input. See "this
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section"_Section_howto.html#howto_15 for an overview of LAMMPS output
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options.
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The output for {dist} will be in distance "units"_units.html. The
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output for {eng} will be in energy "units"_units.html. The output for
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{force} will be in force "units"_units.html.
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[Restrictions:] none
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[Related commands:]
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"dump local"_dump.html, "compute
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property/local"_compute_property_local.html
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[Default:] none
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