forked from lijiext/lammps
129 lines
5.5 KiB
Plaintext
129 lines
5.5 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/local command :h3
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[Syntax:]
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compute ID group-ID property/local input1 input2 ... :pre
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ID, group-ID are documented in "compute"_compute.html command :ulb,l
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property/local = style name of this compute command :l
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input = one or more attributes :l
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possible attributes = natom1 natom2
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patom1 patom2
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batom1 batom2 btype
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aatom1 aatom2 aatom3 atype
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datom1 datom2 datom3 dtype
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iatom1 iatom2 iatom3 itype :pre
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natom1, natom2 = IDs of 2 atoms in each pair (within neighbor cutoff)
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patom1, patom2 = IDs of 2 atoms in each pair (within force cutoff)
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batom1, batom2 = IDs of 2 atoms in each bond
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btype = bond type of each bond
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aatom1, aatom2, aatom3 = IDs of 3 atoms in each angle
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atype = angle type of each angle
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datom1, datom2, datom3, datom4 = IDs of 4 atoms in each dihedral
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dtype = dihedral type of each dihedral
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iatom1, iatom2, iatom3, iatom4 = IDs of 4 atoms in each improper
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itype = improper type of each improper :pre
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:ule
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[Examples:]
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compute 1 all property/local btype batom1 batom2
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compute 1 all property/local atype aatom2 :pre
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[Description:]
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Define a computation that stores the specified attributes as local
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data so it can be accessed by other "output
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commands"_Section_howto.html#4_15. If the input attributes refer to
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bond information, then the number of datums generated, aggregated
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across all processors, equals the number of bonds in the system.
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Ditto for pairs, angles, etc.
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If multiple input attributes are specified then they must all generate
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the same amount of information, so that the resulting local array has
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the same number of rows for each column. This means that only bond
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attributes can be specified together, or angle attributes, etc. Bond
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and angle attributes can not be mixed in the same compute
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property/local command.
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If the inputs are pair attributes, the local data is generated by
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looping over the pairwise neighbor list. Info about an individual
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pairwise interaction will only be included if both atoms in the pair
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are in the specified compute group. For {natom1} and {natom2}, all
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atom pairs in the neighbor list are considered (out to the neighbor
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cutoff = force cutoff + "neighbor skin"_neighbor.html). For {patom1}
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and {patom2}, the distance between the atoms must be less than the
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force cutoff distance for that pair to be included, 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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If the inputs are bond, angle, etc attributes, the local data is
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generated by looping over all the atoms owned on a processor and
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extracting bond, angle, etc info. For bonds, info about an individual
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bond will only be included if both atoms in the bond are in the
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specified compute group. Likewise for angles, dihedrals, etc.
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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, output from the "compute
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bond/local"_compute_bond_local.html command can be combined with bond
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atom indices from this command and output by the "dump
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local"_dump.html command in a consistent way.
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The {natom1} and {natom2}, or {patom1} and {patom2} attributes refer
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to the atom IDs of the 2 atoms in each pairwise interaction computed
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by the "pair_style"_pair_style.html command.
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IMPORTANT NOTE: For pairs, if two atoms I,J are involved in 1-2, 1-3,
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1-4 interactions within the molecular topology, their pairwise
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interaction may be turned off, and thus they may not appear in the
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neighbor list, and will not be part of the local data created by this
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command. More specifically, this may be true of I,J pairs with a
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weighting factor of 0.0; pairs with a non-zero weighting factor are
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included. The weighting factors for 1-2, 1-3, and 1-4 pairwise
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interactions are set by the "special_bonds"_special_bonds.html
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command.
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The {batom1} and {batom2} attributes refer to the atom IDs of the 2
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atoms in each "bond"_bond_style.html. The {btype} attribute refers to
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the type of the bond, from 1 to Nbtypes = # of bond types. The number
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of bond types is defined in the data file read by the
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"read_data"_read_data.html command. The attributes that start with
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"a", "d", "i", refer to similar values for "angles"_angle_style.html,
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"dihedrals"_dihedral_style.html, and "impropers"_improper_style.html.
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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 input values. The length of the vector or number of rows in
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the array is the number of bonds, angles, etc. If a single input is
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specified, a local vector is produced. If two or more inputs are
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specified, a local array is produced where the number of columns = the
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number of inputs. The vector or array can be accessed by any command
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that uses local values from a compute as input. See "this
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section"_Section_howto.html#4_15 for an overview of LAMMPS output
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options.
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The vector or array values will be integers that correspond to the
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specified attribute.
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[Restrictions:] none
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[Related commands:]
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"dump local"_dump.html, "compute reduce"_compute_reduce.html
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[Default:] none
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