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

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

:line

compute pair command :h3

[Syntax:]

compute ID group-ID pair pstyle \[nstyle\] \[evalue\]  :pre

ID, group-ID are documented in "compute"_compute.html command :ulb,l
pair = style name of this compute command :l
pstyle = style name of a pair style that calculates additional values :l
nsub = {n}-instance of a sub-style, if a pair style is used multiple times in a hybrid style :l
{evalue} = {epair} or {evdwl} or {ecoul} or blank (optional) :l
:ule

[Examples:]

compute 1 all pair gauss
compute 1 all pair lj/cut/coul/cut ecoul
compute 1 all pair tersoff 2 epair
compute 1 all pair reax/c :pre

[Description:]

Define a computation that extracts additional values calculated by a
pair style, and makes them accessible for output or further processing
by other commands.

NOTE: 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. If the sub-style is
used more than once, an additional number {nsub} has to be specified
in order to choose which instance of the sub-style will be used by
the compute. Not specifying the number in this case will cause the
compute to fail.

The {evalue} setting is optional.  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 blank or specified as {epair}, 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
specified 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 14 components is tallied by the "pair_style
reax/c"_pair_reaxc.html command.  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 the "Howto output"_Howto_output.html doc
page 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 keyword defaults are {evalue} = {epair}, nsub = 0.
