forked from lijiext/lammps
84 lines
3.2 KiB
HTML
84 lines
3.2 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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<H3>compute inertia/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 inertia/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>inertia/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 inertia/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 inertia tensor of individual
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molecules. The calculation includes all effects due to atoms passing
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thru periodic boundaries.
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</P>
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<P>The symmetric intertia tensor has 6 components, ordered
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Ixx,Iyy,Izz,Ixy,Iyz,Ixz. The tensor for a particular molecule is only
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computed if one or more of its atoms is in the specified group.
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Normally all atoms in the molecule should be in the group, however
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this is not required. LAMMPS will warn you if this is not the case.
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Only atoms in the group contribute to the inertia tensor and
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associated center-of-mass 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, the 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>IMPORTANT NOTE: The coordinates of an atom contribute to the
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molecule's inertia tensor in "unwrapped" form, by using the image
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flags associated with each atom. See the <A HREF = "dump.html">dump custom</A>
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command for a discussion of "unwrapped" coordinates. See the Atoms
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section of the <A HREF = "read_data.html">read_data</A> command for a discussion of
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image flags and how they are set for each atom. You can reset the
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image flags (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>IMPORTANT NOTE: If an atom is part of a rigid body (see the <A HREF = "fix_rigid.html">fix
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rigid</A> command), it's periodic image flags are altered,
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and its contribution to the inertia tensor may not reflect its true
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contribution. See the <A HREF = "fix_rigid.html">fix rigid</A> command for details.
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Thus, to compute the inertia tensor of rigid bodies as they cross
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periodic boundaries, you will need to post-process a <A HREF = "dump.html">dump
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file</A> containing coordinates of the atoms in the bodies.
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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 = 6 for the 6 components of the
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inertia tensor of each molecule, ordered as listed above. These
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values can be accessed by any command that uses global array values
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from a compute as input. See <A HREF = "Section_howto.html#howto_15">Section_howto
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15</A> for an overview of LAMMPS output
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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 = "variable.html">variable inertia() function</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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