2009-12-04 08:52:20 +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 gyration 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 gyration
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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>gyration = style name of this compute command
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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 molecule gyration
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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 radius of gyration Rg of the
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group of atoms, including all effects due to atoms passing thru
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periodic boundaries.
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</P>
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<P>Rg is a measure of the size of the group of atoms, and is computed by
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this formula
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</P>
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<CENTER><IMG SRC = "Eqs/compute_gyration.jpg">
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</CENTER>
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2009-12-22 01:34:52 +08:00
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<P>where M is the total mass of the group, Rcm is the center-of-mass
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position of the group, and the sum is over all atoms in the group.
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2009-12-04 08:52:20 +08:00
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</P>
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<P>IMPORTANT NOTE: The coordinates of an atom contribute to Rg in
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"unwrapped" form, by using the image flags associated with each atom.
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See the <A HREF = "dump.html">dump custom</A> command for a discussion of
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"unwrapped" coordinates. See the Atoms section of the
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<A HREF = "read_data.html">read_data</A> command for a discussion of image flags and
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how they are set for each atom. You can reset the image flags
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(e.g. to 0) before invoking this compute by using the <A HREF = "set.html">set
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image</A> command.
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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 (Rg). This value can be used
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by any command that uses a global scalar value from a compute as
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input. See <A HREF = "Section_howto.html#4_15">this section</A> for an overview of
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LAMMPS output options.
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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 "intensive". The
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scalar value will be in distance <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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2009-12-04 08:52:20 +08:00
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<P><B>Restrictions:</B> none
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</P>
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2009-12-22 01:34:52 +08:00
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<P><B>Related commands:</B>
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</P>
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<P><A HREF = "compute_gyration_molecule.html">compute gyration/molecule</A>
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2009-12-04 08:52:20 +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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