2007-11-02 00:46:50 +08:00
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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 pe command
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</H3>
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2011-06-09 05:46:03 +08:00
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<H3>compute pe/cuda command
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</H3>
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2007-11-02 00:46:50 +08:00
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<P><B>Syntax:</B>
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</P>
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<PRE>compute ID group-ID pe keyword ...
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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>pe = style name of this compute command
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2007-11-03 05:05:48 +08:00
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<LI>zero or more keywords may be appended
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2007-11-02 00:46:50 +08:00
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<LI>keyword = <I>pair</I> or <I>bond</I> or <I>angle</I> or <I>dihedral</I> or <I>improper</I> or <I>kspace</I>
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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 pe
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2007-12-01 07:16:45 +08:00
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compute molPE all pe bond angle dihedral improper
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2007-11-02 00:46:50 +08:00
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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 calculates the potential energy of the
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entire system of atoms. The specified group must be "all". See the
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2007-12-01 07:16:45 +08:00
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<A HREF = "compute_pe_atom.html">compute pe/atom</A> command if you want per-atom
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2007-11-02 00:46:50 +08:00
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energies. These per-atom values could be summed for a group of atoms
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2008-02-26 00:06:38 +08:00
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via the <A HREF = "compute_reduce.html">compute reduce</A> command.
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2007-11-02 00:46:50 +08:00
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</P>
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2008-03-01 09:13:20 +08:00
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<P>The energy is calculated by the various pair, bond, etc potentials
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2007-11-02 00:46:50 +08:00
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defined for the simulation. If no extra keywords are listed, then the
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potential energy is the sum of pair, bond, angle, dihedral, improper,
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and kspace (long-range) energy. If any extra keywords are listed,
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then only those components are summed to compute the potential energy.
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</P>
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<P>Various fixes can contribute to the total potential energy of the
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system. See the doc pages for <A HREF = "fix.html">individual fixes</A> for
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details. The <I>thermo</I> option of the
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<A HREF = "compute_modify.html">compute_modify</A> command determines whether these
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contributions are added into the computed potential energy. If no
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keywords are specified the default is <I>yes</I>. If any keywords are
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specified, the default is <I>no</I>.
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</P>
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<P>A compute of this style with the ID of "thermo_pe" is created when
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LAMMPS starts up, as if this command were in the input script:
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</P>
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<PRE>compute thermo_pe all pe
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</PRE>
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<P>See the "thermo_style" command for more details.
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</P>
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2011-06-09 05:46:03 +08:00
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<HR>
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<P>Styles with a <I>cuda</I> suffix are functionally the same as the
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corresponding style without the suffix. They have been optimized to
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run faster, depending on your available hardware, as discussed in
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<A HREF = "Section_accelerate.html">this section</A> of the manual. The accelerated
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styles take the same arguments and should produce the same results,
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except for round-off and precision issues.
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</P>
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<P>These accelerated styles are part of the "user-cuda" package. They
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are only enabled if LAMMPS was built with that package. See the
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2011-08-26 00:46:23 +08:00
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<A HREF = "Section_start.html#start_3">Making LAMMPS</A> section for more info.
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2011-06-09 05:46:03 +08:00
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</P>
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<P>You can specify the accelerated styles explicitly in your input script
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2011-08-26 00:46:23 +08:00
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by including their suffix, or you can use the <A HREF = "Section_start.html#start_6">-suffix command-line
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switch</A> when you invoke LAMMPS, or you can
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use the <A HREF = "suffix.html">suffix</A> command in your input script.
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2011-06-09 05:46:03 +08:00
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</P>
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<P>See <A HREF = "Section_accelerate.html">this section</A> of the manual for more
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instructions on how to use the accelerated styles effectively.
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</P>
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<HR>
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2008-01-03 03:25:15 +08:00
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<P><B>Output info:</B>
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</P>
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2009-12-04 07:58:11 +08:00
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<P>This compute calculates a global scalar (the potential energy). This
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value can be used by any command that uses a global scalar value from
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2011-08-26 01:01:01 +08:00
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a compute as input. See <A HREF = "Section_howto.html#howto_15">this section</A>
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for an overview of LAMMPS output options.
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2009-12-04 07:58:11 +08:00
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</P>
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2010-03-03 05:51:16 +08:00
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<P>The scalar value calculated by this compute is "extensive". The
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scalar value will be in energy <A HREF = "units.html">units</A>.
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2010-01-24 07:20:05 +08:00
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</P>
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2007-11-02 00:46:50 +08:00
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<P><B>Restrictions:</B> none
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</P>
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2007-12-01 07:16:45 +08:00
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<P><B>Related commands:</B>
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</P>
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<P><A HREF = "compute_pe_atom.html">compute pe/atom</A>
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2007-11-02 00:46:50 +08:00
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</P>
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<P><B>Default:</B> none
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</P>
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</HTML>
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