forked from lijiext/lammps
97 lines
3.5 KiB
HTML
97 lines
3.5 KiB
HTML
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<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>fix coord/original command
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</H3>
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<P><B>Syntax:</B>
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</P>
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<PRE>fix ID group-ID coord/original keyword values ...
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</PRE>
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<UL><LI>ID, group-ID are documented in <A HREF = "fix.html">fix</A> command
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<LI>coord/original = style name of this fix command
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<LI>zero or more keyword/value pairs may be appended
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<LI>keyword = <I>com</I>
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<PRE> <I>com</I> value = <I>yes</I> or <I>no</I>
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</PRE>
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</UL>
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<P><B>Examples:</B>
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</P>
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<PRE>fix 1 all coord/original
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fix 1 upper coord/original com yes
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</PRE>
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<P><B>Description:</B>
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</P>
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<P>Store the original coordinates of atoms in the group at the time the
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fix command is issued. This is used for computing a displacement of
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the atoms at later times, via the <A HREF = "compute_displace_atom.html">compute
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displace/atom</A> command. Or the original
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coordinates can be accessed by other <A HREF = "Section_howto.html#4_15">output
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commands</A> that use per-atom quantities such as
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the <A HREF = "dump.html">dump custom</A> command.
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</P>
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<P>IMPORTANT NOTE: The original coordinates are stored in "unwrapped"
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form, by using the image flags associated with each atom. See the
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<A HREF = "dump.html">dump custom</A> command for a discussion of "unwrapped"
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coordinates. See the Atoms section of the <A HREF = "read_data.html">read_data</A>
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command for a discussion of image flags and how they are set for each
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atom. You can reset the image flags (e.g. to 0) before invoking this
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fix by using the <A HREF = "set.html">set 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 original coordinates may not be what you expect. See the
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<A HREF = "fix_rigid.html">fix rigid</A> command for details.
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</P>
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<P>If the <I>com</I> keyword is set to <I>yes</I> then the position
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of each atom relative to the center-of-mass of the group of
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atoms is stored, instead of the absolute position. This option
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is used by the <A HREF = "compute_msd.html">compute msd</A> command.
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</P>
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<P><B>Restart, fix_modify, output, run start/stop, minimize info:</B>
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</P>
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<P>This fix writes the original coordinates of the atoms to <A HREF = "restart.html">binary
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restart files</A>, so that the values can be restored when a
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simulation is restarted. See the <A HREF = "read_restart.html">read_restart</A>
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command for info on how to re-specify a fix in an input script that
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reads a restart file, so that the operation of the fix continues in an
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uninterrupted fashion.
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</P>
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<P>None of the <A HREF = "fix_modify.html">fix_modify</A> options are relevant to this
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fix.
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</P>
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<P>This fix produces a per-atom array which can be accessed by various
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<A HREF = "Section_howto.html#4_15">output commands</A>. The number of columns
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for each atom is 3, and the columns store the original unwrapped
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x,y,z coords of each atom. The per-atom values be accessed on any
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timestep.
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</P>
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<P>No parameter of this fix can be used with the <I>start/stop</I> keywords of
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the <A HREF = "run.html">run</A> command. This fix is not invoked during <A HREF = "minimize.html">energy
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minimization</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_msd.html">compute msd</A>, <A HREF = "compute_displace_atom.html">compute
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displace/atom</A>
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</P>
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<P><B>Default:</B>
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</P>
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<P>The option default is com = no.
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</P>
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</HTML>
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