"LAMMPS WWW Site"_lws - "LAMMPS Documentation"_ld - "LAMMPS Commands"_lc :c

:link(lws,http://lammps.sandia.gov)
:link(ld,Manual.html)
:link(lc,Section_commands.html#comm)

:line

compute pair command :h3

[Syntax:]

compute ID group-ID pair pstyle evalue :pre

ID, group-ID are documented in "compute"_compute.html command
pair = style name of this compute command
pstyle = style name of a pair style that calculates additional values
evalue = {epair} or {evdwl} or {ecoul} or blank (optional setting) :ul

[Examples:]

compute 1 all pair gauss
compute 1 all pair lj/cut/coul/cut ecoul
compute 1 all pair reax :pre

[Description:]

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.

The specified {pstyle} must be a pair style used in your simulation
either by itself or as a sub-style in a "pair_style hybrid or
hybrid/overlay"_pair_hybrid.html command.

The {evalue} setting is optional; it may be left off the command.  All
pair styles tally a potential energy {epair} which may be broken into
two parts: {evdwl} and {ecoul} such that {epair} = {evdwl} + {ecoul}.
If the pair style calculates Coulombic interactions, their energy will
be tallied in {ecoul}.  Everything else (whether it is a Lennard-Jones
style van der Waals interaction or not) is tallied in {evdwl}.  If
{evalue} is specified as {epair} or left out, then {epair} is stored
as a global scalar by this compute.  This is useful when using
"pair_style hybrid"_pair_hybrid.html if you want to know the portion
of the total energy contributed by one sub-style.  If {evalue} is
specfied as {evdwl} or {ecoul}, then just that portion of the energy
is stored as a global scalar.

NOTE: The energy returned by the {evdwl} keyword does not include tail
corrections, even if they are enabled via the
"pair_modify"_pair_modify.html command.

Some pair styles tally additional quantities, e.g. a breakdown of
potential energy into a dozen or so components is tallied by the
"pair_style reax"_pair_reax.html commmand.  These values (1 or more)
are stored as a global vector by this compute.  See the doc page for
"individual pair styles"_pair_style.html for info on these values.

[Output info:]

This compute calculates a global scalar which is {epair} or {evdwl} or
{ecoul}.  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 "this
section"_Section_howto.html#howto_15 for an overview of LAMMPS output
options.

The scalar and vector values calculated by this compute are
"extensive".

The scalar value will be in energy "units"_units.html.  The vector
values will typically also be in energy "units"_units.html, but
see the doc page for the pair style for details.

[Restrictions:] none

[Related commands:]

"compute pe"_compute_pe.html, "compute bond"_compute_bond.html

[Default:]

The default for {evalue} is {epair}.