forked from lijiext/lammps
66 lines
2.2 KiB
HTML
66 lines
2.2 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 vcm/molecule 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 vcm/molecule
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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>vcm/molecule = 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 fluid vcm/molecule
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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 center-of-mass velocity of
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individual molecules. The x,y,z components of the velocity of each
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molecule are computed. This is calcualted by summing mass*velocity
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for each atom in the molecule and dividing the sum by the total mass
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of the molecule.
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</P>
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<P>The velocity of a particular molecule is only computed if one or more
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of its atoms are in the specified group. Normally all atoms in the
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molecule should be in the group, however this is not required. LAMMPS
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will warn you if this is not the case. Only atoms in the group
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contribute to the velocity calculation for the molecule.
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</P>
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<P>The ordering of per-molecule quantities produced by this compute is
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consistent with the ordering produced by other compute commands that
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generate per-molecule datums. Conceptually, them molecule IDs will be
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in ascending order for any molecule with one or more of its atoms in
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the specified group.
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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 array where the number of rows =
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Nmolecules and the number of columns = 3 for the vx,vy,vz components
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of the center-of-mass velocity of each molecule. These values can be
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accessed by any command that uses global array values from a compute
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as input. See <A HREF = "Section_howto.html#howto_15">Section_howto 15</A> for an
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overview of LAMMPS output options.
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</P>
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<P>The array values are "intensive". The array values will be in
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distance <A HREF = "units.html">units</A>.
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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_atom_molecule.html">compute atom/molecule</A>
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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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