2007-03-27 05:33:10 +08:00
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"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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communicate command :h3
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[Syntax:]
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2008-02-15 07:13:41 +08:00
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communicate style keyword value ... :pre
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2007-03-27 05:33:10 +08:00
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2008-02-15 07:13:41 +08:00
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style = {single} or {multi} :ulb,l
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zero or more keyword/value pairs may be appended :l
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2009-11-10 02:30:55 +08:00
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keyword = {cutoff} or {group} or {vel} :l
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{cutoff} value = Rcut (distance units) = communicate atoms from this far away
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2008-08-21 21:53:06 +08:00
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{group} value = group-ID = only communicate atoms in the group
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2009-11-10 02:30:55 +08:00
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{vel} value = {yes} or {no} = do or do not communicate velocity info with ghost atoms :pre
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2008-02-15 07:13:41 +08:00
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:ule
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2007-03-27 05:33:10 +08:00
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[Examples:]
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2008-02-15 07:13:41 +08:00
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communicate multi
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2008-08-21 21:53:06 +08:00
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communicate multi group solvent
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2010-01-15 03:44:28 +08:00
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communicate single vel yes
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communicate single cutoff 5.0 vel yes :pre
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2007-03-27 05:33:10 +08:00
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[Description:]
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This command sets the style of inter-processor communication that
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occurs each timestep as atom coordinates and other properties are
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2008-02-16 03:09:18 +08:00
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exchanged between neighboring processors and stored as properties of
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ghost atoms.
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2007-03-27 05:33:10 +08:00
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The default style is {single} which means each processor acquires
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information for ghost atoms that are within a single distance from its
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sub-domain. The distance is the maximum of the neighbor cutoff for
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all atom type pairs.
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For many systems this is an efficient algorithm, but for systems with
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widely varying cutoffs for different type pairs, the {multi} style can
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be faster. In this case, each atom type is assigned its own distance
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cutoff for communication purposes, and fewer atoms will be
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communicated. See the "neighbor multi"_neighbor.html command for a
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neighbor list construction option that may also be beneficial for
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simulations of this kind.
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2008-08-21 22:03:21 +08:00
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The {cutoff} option allows you to set a ghost cutoff distance, which
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is the distance from the borders of a processor's sub-domain at which
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2008-08-21 21:53:06 +08:00
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ghost atoms are acquired from other processors. By default the ghost
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2008-08-21 22:03:21 +08:00
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cutoff = neighbor cutoff = pairwise force cutoff + neighbor skin. See
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the "neighbor"_neighbor.html command for more information about the
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skin distance. If the specified Rcut is greater than the neighbor
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cutoff, then extra ghost atoms will be acquired. If it is smaller,
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the ghost cutoff is set to the neighbor cutoff.
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2008-08-21 21:53:06 +08:00
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These are simulation scenarios in which it may be useful to set a
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ghost cutoff > neighbor cutoff:
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a single polymer chain with bond interactions, but no pairwise interactions
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bonded interactions (e.g. dihedrals) extend further than the pairwise cutoff
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ghost atoms beyond the pairwise cutoff are needed for some computation :ul
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In the first scenario, a pairwise potential may not be defined. Thus
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the pairwise neighbor cutoff will be 0.0. But ghost atoms are still
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needed for computing bond, angle, etc interactions between atoms on
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different processors. The appropriate ghost cutoff depends on the
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"newton bond"_newton.html setting. For newton bond {off}, the
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distance needs to be the furthest distance between any two atoms in
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the bond, angle, etc. E.g. the distance between 1-4 atoms in a
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dihedral. For newton bond {on}, the distance between the central atom
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in the bond, angle, etc and any other atom is sufficient. E.g. the
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distance between 2-4 atoms in a dihedral.
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In the second scenario, a pairwise potential is defined, but its
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neighbor cutoff is not sufficiently long enough to enable bond, angle,
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etc terms to be computed. As in the previous scenario, an appropriate
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ghost cutoff should be set.
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In the last scenario, a "fix"_fix.html or "compute"_compute.html or
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"pairwise potential"_pair_style.html needs to calculate with ghost
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atoms beyond the normal pairwise cutoff for some computation it
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performs (e.g. locate neighbors of ghost atoms in a multibody pair
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potential). Setting the ghost cutoff appropriately can insure it will
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find the needed atoms.
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2009-11-10 02:30:55 +08:00
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The {group} option will limit communication to atoms in the specified
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group. This can be useful for models where no ghost atoms are needed
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for some kinds of particles. All atoms (not just those in the
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specified group) will still migrate to new processors as they move.
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The group specified with this option must also be specified via the
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"atom_modify first"_atom_modify.html command.
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The {vel} option enables velocity information to be communicated with
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ghost particles. Depending on the "atom_style"_atom_style.html,
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velocity info includes the translational velocity, angular velocity,
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and angular momentum of a particle. If the {vel} option is set to
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{yes}, then ghost atoms store these quantities; if {no} then they do
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not. The {yes} setting is needed by some pair styles which require
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the velocity state of both the I and J particles to compute a pairwise
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I,J interaction.
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2011-03-08 07:01:59 +08:00
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Note that if the "fix deform"_fix_deform.html command is being used
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with its "remap v" option enabled, then the velocities for ghost atoms
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(in the fix deform group) mirrored across a periodic boundary will
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also include components due to any velocity shift that occurs across
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that boundary (e.g. due to dilation or shear).
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2007-03-27 05:33:10 +08:00
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[Restrictions:] none
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[Related commands:]
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"neighbor"_neighbor.html
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[Default:]
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2009-11-10 02:30:55 +08:00
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The default settings are style = single, group = all, cutoff = 0.0,
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2010-06-15 22:02:14 +08:00
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vel = no. The cutoff default of 0.0 means that ghost cutoff =
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2008-08-21 22:03:21 +08:00
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neighbor cutoff = pairwise force cutoff + neighbor skin.
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