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rLAMMPS lammps
compute_pair.html
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<HTML>
<CENTER><A
HREF =
"http://lammps.sandia.gov"
>
LAMMPS WWW Site
</A>
-
<A
HREF =
"Manual.html"
>
LAMMPS Documentation
</A>
-
<A
HREF =
"Section_commands.html#comm"
>
LAMMPS Commands
</A>
</CENTER>
<HR>
<H3>
compute pair command
</H3>
<P><B>
Syntax:
</B>
</P>
<PRE>
compute ID group-ID pair pstyle evalue
</PRE>
<UL><LI>
ID, group-ID are documented in
<A
HREF =
"compute.html"
>
compute
</A>
command
<LI>
pair = style name of this compute command
<LI>
pstyle = style name of a pair style that calculates additional values
<LI>
evalue =
<I>
epair
</I>
or
<I>
evdwl
</I>
or
<I>
ecoul
</I>
or blank (optional setting)
</UL>
<P><B>
Examples:
</B>
</P>
<PRE>
compute 1 all pair gauss
compute 1 all pair lj/cut/coul/cut ecoul
compute 1 all pair reax
</PRE>
<P><B>
Description:
</B>
</P>
<P>
Define a computation that extracts additional values calculated by a
pair style, sums them across processors, and makes them accessible for
output or further processing by other commands. The group specified
for this command is ignored.
</P>
<P>
The specified
<I>
pstyle
</I>
must be a pair style used in your simulation
either by itself or as a sub-style in a
<A
HREF =
"pair_hybrid.html"
>
pair_style hybrid or
hybrid/overlay
</A>
command.
</P>
<P>
The
<I>
evalue
</I>
setting is optional; it may be left off the command. All
pair styles tally a potential energy
<I>
epair
</I>
which may be broken into
two parts:
<I>
evdwl
</I>
and
<I>
ecoul
</I>
such that
<I>
epair
</I>
=
<I>
evdwl
</I>
+
<I>
ecoul
</I>
.
If the pair style calculates Coulombic interactions, their energy will
be tallied in
<I>
ecoul
</I>
. Everything else (whether it is a Lennard-Jones
style van der Waals interaction or not) is tallied in
<I>
evdwl
</I>
. If
<I>
evalue
</I>
is specified as
<I>
epair
</I>
or left out, then
<I>
epair
</I>
is stored
as a global scalar by this compute. This is useful when using
<A
HREF =
"pair_hybrid.html"
>
pair_style hybrid
</A>
if you want to know the portion
of the total energy contributed by one sub-style. If
<I>
evalue
</I>
is
specfied as
<I>
evdwl
</I>
or
<I>
ecoul
</I>
, then just that portion of the energy
is stored as a global scalar.
</P>
<P>
Some pair styles tally additional quantities, e.g. a breakdown of
potential energy into a dozen or so components is tallied by the
<A
HREF =
"pair_reax.html"
>
pair_style reax
</A>
commmand. These values (1 or more)
are stored as a global vector by this compute. See the doc page for
<A
HREF =
"pair_style.html"
>
individual pair styles
</A>
for info on these values.
</P>
<P><B>
Output info:
</B>
</P>
<P>
This compute calculates a global scalar which is
<I>
epair
</I>
or
<I>
evdwl
</I>
or
<I>
ecoul
</I>
. If the pair style supports it, it also calculates a global
vector of length >= 1, as determined by the pair style. These values
can be used by any command that uses global scalar or vector values
from a compute as input. See
<A
HREF =
"Section_howto.html#howto_15"
>
this
section
</A>
for an overview of LAMMPS output
options.
</P>
<P>
The scalar and vector values calculated by this compute are
"extensive".
</P>
<P>
The scalar value will be in energy
<A
HREF =
"units.html"
>
units
</A>
. The vector
values will typically also be in energy
<A
HREF =
"units.html"
>
units
</A>
, but
see the doc page for the pair style for details.
</P>
<P><B>
Restrictions:
</B>
none
</P>
<P><B>
Related commands:
</B>
</P>
<P><A
HREF =
"compute_pe.html"
>
compute pe
</A>
</P>
<P><B>
Default:
</B>
</P>
<P>
The default for
<I>
evalue
</I>
is
<I>
epair
</I>
.
</P>
</HTML>
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