fa37609d36
git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@13959 f3b2605a-c512-4ea7-a41b-209d697bcdaa
93 lines
3.3 KiB
HTML
93 lines
3.3 KiB
HTML
<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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</CENTER>
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<HR>
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<H3>compute force/tally command
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</H3>
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<H3>compute heat/flux/tally command
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</H3>
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<H3>compute pe/tally command
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</H3>
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<H3>compute stress/tally 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 style group2-ID
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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>style = <I>force/tally</I> or <I>pe/tally</I> or <I>stress/tally</I>
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<LI>group2-ID = group ID of second (or same) group
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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 lower force/tally upper
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compute 1 left pe/tally right
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compute 1 lower stress/tally lower
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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 properties between two groups of
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atoms by accumulating them from pairwise non-bonded computations. The
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two groups can be the same. This is similar to <A HREF = "compute_group_group.html">compute
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group/group</A> only that the data is
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accumulated directly during the non-bonded force computation. The
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computes <I>force/tally</I>, <I>pe/tally</I>, <I>stress/tally</I>, and
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<I>heat/flux/tally</I> are primarily provided as example how to program
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additional, more sophisticated computes using the tally mechanism.
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</P>
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<HR>
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<P>The pairwise contributions are computing via a callback that the
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compute registers with the non-bonded pairwise force computation.
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This limits the use to systems that have no bonds, no Kspace, and no
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manybody interactions. On the other hand, the computation does not
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have to compute forces or energies a second time and thus can be much
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more efficient. The callback mechanism allows to write more complex
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pairwise property computations.
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</P>
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<HR>
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<P><B>Output info:</B>
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</P>
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<P>Compute <I>pe/tally</I> calculates a global scalar (the energy) and a per
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atom scalar (the contributions of the single atom to the global
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scalar). Compute <I>force/tally</I> calculates a global scalar (the force
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magnitude) and a per atom 3-element vector (force contribution from
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each atom). Compute <I>stress/tally</I> calculates a global scalar
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(average of the diagonal elements of the stress tensor) and a per atom
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vector (the 6 elements of stress tensor contributions from the
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individual atom).
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</P>
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<P>Both 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><B>Restrictions:</B>
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</P>
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<P>This compute is part of the USER-TALLY package. It is only enabled
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if LAMMPS was built with that package. See the <A HREF = "Section_start.html#start_3">Making
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LAMMPS</A> section for more info.
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</P>
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<P>Not all pair styles can be evaluated in a pairwise mode as required by
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this compute. For example, 3-body and other many-body potentials,
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such as <A HREF = "pair_tersoff.html">Tersoff</A> and
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<A HREF = "pair_sw.html">Stillinger-Weber</A> cannot be used. <A HREF = "pair_eam.html">EAM</A>
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potentials only include the pair potential portion of the EAM
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interaction when used by this compute, not the embedding term. Also
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bonded or Kspace interactions do not contribute to this compute.
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</P>
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<P><B>Related commands:</B>
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</P>
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<P><I>compute group/group</I>_compute_group_group.html, <I>compute
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heat/flux</I>_compute_heat_flux.html
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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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