<LI>zero or more keyword/value pairs may be appended 

<LI>keyword = <I>group</I> 

<LI>keyword = <I>group</I> or <I>cutoff</I> 

<PRE>  <I>group</I> value = group-ID = only communicate atoms in the group

  <I>cutoff</I> value = Rcut (distance units) = communicate atoms from this far away 

</PRE>

</UL>

</P>

<PRE>communicate multi

communicate multi group solvent

communicate single cutoff 5.0 

</PRE>

<P><B>Description:</B>

</P>

The group specified with this option must also be specified via the

<A HREF = "atom_modify.html">atom_modify first</A> command.

</P>

<P>The <I>cutoff</I> option allows you to set a ghost cutoff distance which is

the distance from the borders of a processor's sub-domain at which

ghost atoms are acquired from other processors.  By default the ghost

cutoff = the neighbor cutoff = the pairwise force cutoff + the

neighbor skin.  See the <A HREF = "neighbor.html">neighbor</A> command for more

information about the skin distance.  If the specified Rcut is greater

than the neighbor cutoff, then extra ghost atoms will be acquired.  If

it is smaller, the ghost cutoff is set to the neighbor cutoff.

</P>

<P>These are simulation scenarios in which it may be useful to set a

ghost cutoff > neighbor cutoff:

</P>

<UL><LI>a single polymer chain with bond interactions, but no pairwise interactions

<LI>bonded interactions (e.g. dihedrals) extend further than the pairwise cutoff

<LI>ghost atoms beyond the pairwise cutoff are needed for some computation 

</UL>

<P>In the first scenario, a pairwise potential may not be defined.  Thus

the pairwise neighbor cutoff will be 0.0.  But ghost atoms are still

needed for computing bond, angle, etc interactions between atoms on

different processors.  The appropriate ghost cutoff depends on the

<A HREF = "newton.html">newton bond</A> setting.  For newton bond <I>off</I>, the

distance needs to be the furthest distance between any two atoms in

the bond, angle, etc.  E.g. the distance between 1-4 atoms in a

dihedral.  For newton bond <I>on</I>, the distance between the central atom

in the bond, angle, etc and any other atom is sufficient.  E.g. the

distance between 2-4 atoms in a dihedral.

</P>

<P>In the second scenario, a pairwise potential is defined, but its

neighbor cutoff is not sufficiently long enough to enable bond, angle,

etc terms to be computed.  As in the previous scenario, an appropriate

ghost cutoff should be set.

</P>

<P>In the last scenario, a <A HREF = "fix.html">fix</A> or <A HREF = "compute.html">compute</A> or

<A HREF = "pair_style.html">pairwise potential</A> needs to calculate with ghost

atoms beyond the normal pairwise cutoff for some computation it

performs (e.g. locate neighbors of ghost atoms in a multibody pair

potential).  Setting the ghost cutoff appropriately can insure it will

find the needed atoms.

</P>

<P><B>Restrictions:</B> none

</P>

<P><B>Related commands:</B>

</P>

<P><B>Default:</B>

</P>

<P>The default settings are style = single and group = all.

<P>The default settings are style = single, group = all, cutoff = 0.0.

</P>

</HTML>

style = {single} or {multi} :ulb,l

zero or more keyword/value pairs may be appended :l

keyword = {group} :l

  {group} value = group-ID = only communicate atoms in the group :pre

keyword = {group} or {cutoff} :l

  {group} value = group-ID = only communicate atoms in the group

  {cutoff} value = Rcut (distance units) = communicate atoms from this far away :pre

:ule

[Examples:]

communicate multi

communicate multi group solvent :pre

communicate multi group solvent

communicate single cutoff 5.0 :pre

[Description:]

The group specified with this option must also be specified via the

"atom_modify first"_atom_modify.html command.

The {cutoff} option allows you to set a ghost cutoff distance which is

the distance from the borders of a processor's sub-domain at which

ghost atoms are acquired from other processors.  By default the ghost

cutoff = the neighbor cutoff = the pairwise force cutoff + the

neighbor skin.  See the "neighbor"_neighbor.html command for more

information about the skin distance.  If the specified Rcut is greater

than the neighbor cutoff, then extra ghost atoms will be acquired.  If

it is smaller, the ghost cutoff is set to the neighbor cutoff.

These are simulation scenarios in which it may be useful to set a

ghost cutoff > neighbor cutoff:

a single polymer chain with bond interactions, but no pairwise interactions

bonded interactions (e.g. dihedrals) extend further than the pairwise cutoff

ghost atoms beyond the pairwise cutoff are needed for some computation :ul

In the first scenario, a pairwise potential may not be defined.  Thus

the pairwise neighbor cutoff will be 0.0.  But ghost atoms are still

needed for computing bond, angle, etc interactions between atoms on

different processors.  The appropriate ghost cutoff depends on the

"newton bond"_newton.html setting.  For newton bond {off}, the

distance needs to be the furthest distance between any two atoms in

the bond, angle, etc.  E.g. the distance between 1-4 atoms in a

dihedral.  For newton bond {on}, the distance between the central atom

in the bond, angle, etc and any other atom is sufficient.  E.g. the

distance between 2-4 atoms in a dihedral.

In the second scenario, a pairwise potential is defined, but its

neighbor cutoff is not sufficiently long enough to enable bond, angle,

etc terms to be computed.  As in the previous scenario, an appropriate

ghost cutoff should be set.

In the last scenario, a "fix"_fix.html or "compute"_compute.html or

"pairwise potential"_pair_style.html needs to calculate with ghost

atoms beyond the normal pairwise cutoff for some computation it

performs (e.g. locate neighbors of ghost atoms in a multibody pair

potential).  Setting the ghost cutoff appropriately can insure it will

find the needed atoms.

[Restrictions:] none

[Related commands:]

[Default:]

The default settings are style = single and group = all.

The default settings are style = single, group = all, cutoff = 0.0.

<P>The <I>overlap</I> styles requires inter-processor communication to acquire

ghost atoms and build a neighbor list.  This means that your system

must be ready to perform a simulation before using this command (force

fields setup, atom masses set, etc).

fields setup, atom masses set, etc).  Since a neighbor list is used to

find overlapping atom pairs, it also means that you must define a

<A HREF = "pair_style.html">pair style</A> with force cutoffs greater than or equal

to the desired overlap cutoff between pairs of relevant atom types,

even though the pair potential will not be evaluated.

</P>

<P>If the <A HREF = "special_bonds.html">special_bonds</A> command is used with a

setting of 0, then a pair of bonded atoms (1-2, 1-3, or 1-4) will not

The {overlap} styles requires inter-processor communication to acquire

ghost atoms and build a neighbor list.  This means that your system

must be ready to perform a simulation before using this command (force

fields setup, atom masses set, etc).

fields setup, atom masses set, etc).  Since a neighbor list is used to

find overlapping atom pairs, it also means that you must define a

"pair style"_pair_style.html with force cutoffs greater than or equal

to the desired overlap cutoff between pairs of relevant atom types,

even though the pair potential will not be evaluated.

If the "special_bonds"_special_bonds.html command is used with a

setting of 0, then a pair of bonded atoms (1-2, 1-3, or 1-4) will not

</PRE>

<P><B>Description:</B>

</P>

<P>This command sets parameters that affect the pairwise neighbor list.

<P>This command sets parameters that affect the building and use of

pairwise neighbor lists.

</P>

<P>The <I>every</I>, <I>delay</I>, and <I>check</I> options affect how often the list is

<P>The <I>every</I>, <I>delay</I>, and <I>check</I> options affect how often lists are

built as a simulation runs.  The <I>delay</I> setting means never build a

new list until at least N steps after the previous build.  The <I>every</I>

setting means build the list every M steps (after the delay has