forked from lijiext/lammps
67 lines
2.1 KiB
HTML
67 lines
2.1 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>fix drag 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 drag x y z fmag delta
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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>drag = style name of this fix command
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<LI>x,y,z = coord to drag atoms towards
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<LI>fmag = magnitude of force to apply to each atom (force units)
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<LI>delta = cutoff distance inside of which force is not applied (distance units)
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</UL>
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<P><B>Examples:</B>
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</P>
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<PRE>fix center small-molecule drag 0.0 10.0 0.0 5.0 2.0
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</PRE>
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<P><B>Description:</B>
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</P>
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<P>Apply a force to each atom in a group to drag it towards the point
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(x,y,z). The magnitude of the force is specified by fmag. If an atom
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is closer than a distance delta to the point, then the force is not
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applied.
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</P>
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<P>Any of the x,y,z values can be specified as NULL which means do not
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include that dimension in the distance calculation or force
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application.
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</P>
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<P>This command can be used to steer one or more atoms to a new location
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in the simulation.
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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>No information about this fix is written to <A HREF = "restart.html">binary restart
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files</A>. None of the <A HREF = "fix_modify.html">fix_modify</A> options
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are relevant to this fix.
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</P>
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<P>This fix computes a 3-vector of forces, which can be accessed by
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various <A HREF = "Section_howto.html#4_15">output commands</A>. This is the total
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force on the group of atoms by the drag force. The vector values
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calculated by this fix are "extensive", meaning they scale with the
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number of atoms in the simulation.
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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 = "fix_spring.html">fix spring</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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