2006-09-22 00:22:34 +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>displace_atoms command
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</H3>
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<P><B>Syntax:</B>
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</P>
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<PRE>displace_atoms group-ID style args keyword value ...
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</PRE>
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<UL><LI>group-ID = ID of group of atoms to displace
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<LI>style = <I>move</I> or <I>ramp</I>
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<PRE> <I>move</I> args = delx dely delz
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delx,dely,delz = distance to displace in each dimension (distance units)
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<I>ramp</I> args = ddim dlo dhi dim clo chi
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ddim = <I>x</I> or <I>y</I> or <I>z</I>
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dlo,dhi = displacement distance between dlo and dhi (distance units)
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dim = <I>x</I> or <I>y</I> or <I>z</I>
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clo,chi = lower and upper bound of domain to displace (distance units)
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</PRE>
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<LI>zero or more keyword/value pairs may be appended to the args
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<PRE> keyword = <I>units</I>
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value = <I>box</I> or <I>lattice</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>displace_atoms top move 0 -5 0 units box
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displace_atoms flow ramp x 0.0 5.0 y 2.0 20.5
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</PRE>
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<P><B>Description:</B>
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</P>
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2007-03-21 04:14:06 +08:00
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<P>Displace a group of atoms. This can be used to move atoms a large
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2006-09-22 00:22:34 +08:00
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distance before beginning a simulation. For example, in a shear
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simulation, an initial strain can be imposed on the system. Or two
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groups of atoms can be brought into closer proximity.
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</P>
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<P>The <I>move</I> style displaces the group of atoms by the specified 3d
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distance. The <I>ramp</I> style displaces atoms a variable amount in one
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dimension depending on the atom's coordinate in a (possibly) different
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dimension. For example, the second example command displaces atoms in
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the x-direction an amount between 0.0 and 5.0 distance units. Each
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atom's displacement depends on the fractional distance its y
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coordinate is between 2.0 and 20.5. Atoms with y-coordinates outside
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those bounds will be moved the minimum (0.0) or maximum (5.0) amount.
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</P>
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<P>Distance units for the displacement are determined by the setting of
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<I>box</I> or <I>lattice</I> for the <I>units</I> keyword. <I>Box</I> means distance
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units as defined by the <A HREF = "units.html">units</A> command - e.g. Angstroms
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for <I>real</I> units. <I>Lattice</I> means distance units are in lattice
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spacings. The <A HREF = "lattice.html">lattice</A> command must have been
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previously used to define the lattice spacing.
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2006-09-22 00:22:34 +08:00
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</P>
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<P>Care should be taken not to move atoms on top of other atoms. After
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the move, atoms are remapped to the periodic simulation box. In
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parallel, atoms should not be moved so far that they cross more than
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one processor's sub-domain, else they may be lost. If this is a
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problem, successive displace_atom commands can be used to move atoms a
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large distance.
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</P>
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<P><B>Restrictions:</B>
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</P>
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<P>This command requires inter-processor communication to migrate atoms
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once they have been displaced. This means that your system must be
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ready to perform a simulation before using this command (force fields
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are setup, atom masses are set, etc).
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2006-09-22 00:22:34 +08:00
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</P>
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2006-11-14 06:18:34 +08:00
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<P><B>Related commands:</B>
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</P>
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<P><A HREF = "lattice.html">lattice</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 defaults are units = lattice.
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</P>
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</HTML>
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