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