2006-09-22 00:22:34 +08:00
|
|
|
<HTML>
|
|
|
|
|
<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>
|
|
|
|
|
</CENTER>
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
<HR>
|
|
|
|
|
|
|
|
|
|
<H3>fix indent command
|
|
|
|
|
</H3>
|
|
|
|
|
<P><B>Syntax:</B>
|
|
|
|
|
</P>
|
2007-07-03 04:04:44 +08:00
|
|
|
<PRE>fix ID group-ID indent k keyword values ...
|
2006-09-22 00:22:34 +08:00
|
|
|
</PRE>
|
|
|
|
|
<UL><LI>ID, group-ID are documented in <A HREF = "fix.html">fix</A> command
|
|
|
|
|
|
|
|
|
|
<LI>indent = style name of this fix command
|
|
|
|
|
|
|
|
|
|
<LI>k = force constant for indenter surface (force/distance^2 units)
|
|
|
|
|
|
2007-07-03 04:04:44 +08:00
|
|
|
<LI>one or more keyword/value pairs may be appended
|
2006-09-22 00:22:34 +08:00
|
|
|
|
|
|
|
|
<LI>keyword = <I>sphere</I> or <I>cylinder</I> or <I>vel</I> or <I>rstart</I> or <I>units</I>
|
|
|
|
|
|
|
|
|
|
<PRE> <I>sphere</I> args = x y z R
|
|
|
|
|
x,y,z = initial position of center of indenter
|
|
|
|
|
R = sphere radius of indenter (distance units)
|
|
|
|
|
<I>cylinder</I> args = dim c1 c2 R
|
|
|
|
|
dim = x or y or z = axis of cylinder
|
|
|
|
|
c1,c2 = coords of cylinder axis in other 2 dimensions (distance units)
|
|
|
|
|
R = cylinder radius of indenter (distance units)
|
|
|
|
|
<I>vel</I> args = vx vy vz
|
|
|
|
|
vx,vy,vz = velocity of center of indenter (velocity units)
|
|
|
|
|
<I>rstart</I> value = R0
|
2006-12-13 08:37:25 +08:00
|
|
|
R0 = sphere or cylinder radius at start of run (distance units)
|
2006-09-22 00:22:34 +08:00
|
|
|
R is value at end of run, so indenter expands/contracts over time
|
|
|
|
|
<I>units</I> value = <I>lattice</I> or <I>box</I>
|
|
|
|
|
lattice = the geometry is defined in lattice units
|
|
|
|
|
box = the geometry is defined in simulation box units
|
|
|
|
|
</PRE>
|
|
|
|
|
|
|
|
|
|
</UL>
|
|
|
|
|
<P><B>Examples:</B>
|
|
|
|
|
</P>
|
|
|
|
|
<PRE>fix 1 all indent 10.0 sphere 0.0 0.0 15.0 3.0 vel 0.0 0.0 -1.0
|
|
|
|
|
fix 2 flow indent 10.0 cylinder z 0.0 0.0 10.0 units box
|
|
|
|
|
</PRE>
|
|
|
|
|
<P><B>Description:</B>
|
|
|
|
|
</P>
|
|
|
|
|
<P>Insert an indenter within a simulation box. The indenter repels all
|
|
|
|
|
atoms that touch it, so it can be used to push into a material or as
|
|
|
|
|
an obstacle in a flow.
|
|
|
|
|
</P>
|
|
|
|
|
<P>The indenter can either be spherical or cylindrical. You must set
|
|
|
|
|
one of those 2 keywords.
|
|
|
|
|
</P>
|
|
|
|
|
<P>A spherical indenter exerts a force of magnitude
|
|
|
|
|
</P>
|
|
|
|
|
<PRE>F(r) = - k (r - R)^2
|
|
|
|
|
</PRE>
|
|
|
|
|
<P>on each atom where <I>k</I> is the specified force constant, <I>r</I> is the
|
|
|
|
|
distance from the atom to the center of the indenter, and <I>R</I> is the
|
|
|
|
|
radius of the indenter. The force is repulsive and F(r) = 0 for <I>r</I> >
|
|
|
|
|
<I>R</I>.
|
|
|
|
|
</P>
|
|
|
|
|
<P>A cylindrical indenter exerts the same force, except that <I>r</I> is the
|
|
|
|
|
distance from the atom to the center axis of the cylinder. The
|
|
|
|
|
cylinder extends infinitely along its axis.
|
|
|
|
|
</P>
|
|
|
|
|
<P>If the <I>vel</I> keyword is specified, the center (or axis) of the
|
|
|
|
|
spherical (or cylindrical) indenter will move during the simulation,
|
|
|
|
|
based on its initial position (x,y,z) and the specified (vx,vy,vz).
|
|
|
|
|
Note that if you do multiple runs, the initial position of the
|
|
|
|
|
indenter (x,y,z) does not change, so it will continue to move at the
|
|
|
|
|
specified velocity.
|
|
|
|
|
</P>
|
|
|
|
|
<P>If the <I>rstart</I> keyword is specified, then the radius of the indenter
|
|
|
|
|
is a time-dependent quantity. R0 is the value assigned at the start
|
|
|
|
|
of the run; R is the value at the end. At intermediate times, the
|
2007-06-26 08:03:39 +08:00
|
|
|
radius is linearly interpolated between these two values. This option
|
|
|
|
|
can be used, for example, to grow/shrink a void within the simulation
|
|
|
|
|
box.
|
2006-09-22 00:22:34 +08:00
|
|
|
</P>
|
|
|
|
|
<P>The <I>units</I> keyword determines the meaning of the distance units used
|
|
|
|
|
to define the indenter. A <I>box</I> value selects standard distance units
|
|
|
|
|
as defined by the <A HREF = "units.html">units</A> command, e.g. Angstroms for units
|
|
|
|
|
= real or metal. A <I>lattice</I> value means the distance units are in
|
2006-11-14 06:18:34 +08:00
|
|
|
lattice spacings. The <A HREF = "lattice.html">lattice</A> command must have been
|
|
|
|
|
previously used to define the lattice spacing. Note that the units
|
|
|
|
|
choice affects not only the indenter's physical geometry, but also its
|
|
|
|
|
velocity and force constant since they are defined in terms of
|
|
|
|
|
distance as well.
|
2006-09-22 00:22:34 +08:00
|
|
|
</P>
|
2008-01-18 01:02:19 +08:00
|
|
|
<P>IMPORTANT NOTE: You should insure the indenter's extent does not
|
|
|
|
|
overlap a periodic boundary, either for a fixed indenter, or one that
|
|
|
|
|
moves. No check for such overlaps is performed by the code.
|
|
|
|
|
</P>
|
2007-10-11 06:28:11 +08:00
|
|
|
<P><B>Restart, fix_modify, output, run start/stop, minimize info:</B>
|
2007-06-26 08:03:39 +08:00
|
|
|
</P>
|
|
|
|
|
<P>No information about this fix is written to <A HREF = "restart.html">binary restart
|
|
|
|
|
files</A>.
|
|
|
|
|
</P>
|
|
|
|
|
<P>The <A HREF = "fix_modify.html">fix_modify</A> <I>energy</I> option is supported by this
|
|
|
|
|
fix to add the energy of interaction between atoms and the indenter to
|
|
|
|
|
the system's potential energy as part of <A HREF = "thermo_style.html">thermodynamic
|
|
|
|
|
output</A>. The energy of each particle interacting
|
|
|
|
|
with the indenter is K/3 (r - R)^3.
|
|
|
|
|
</P>
|
2007-10-10 02:24:42 +08:00
|
|
|
<P>This fix computes a scalar energy and a 3-vector of forces (on the
|
|
|
|
|
indenter), which can be accessed by various <A HREF = "Section_howto.html#4_15">output
|
2008-01-03 03:25:15 +08:00
|
|
|
commands</A>. The scalar and vector values
|
|
|
|
|
calculated by this fix are "extensive", meaning they scale with the
|
|
|
|
|
number of atoms in the simulation.
|
2007-06-26 08:03:39 +08:00
|
|
|
</P>
|
|
|
|
|
<P>This fix can adjust the indenter position and radius over multiple
|
|
|
|
|
runs, using the <I>start</I> and <I>stop</I> keywords of the <A HREF = "run.html">run</A>
|
|
|
|
|
command. See the <A HREF = "run.html">run</A> command for details of how to do
|
|
|
|
|
this.
|
|
|
|
|
</P>
|
|
|
|
|
<P>The forces due to this fix are imposed during an energy minimization,
|
|
|
|
|
invoked by the <A HREF = "minimize.html">minimize</A> command. The <I>rstart</I> keyword
|
|
|
|
|
does not change the indenter radius during an energy minimization; the
|
|
|
|
|
indenter always has a radius of its final value R in that case.
|
|
|
|
|
</P>
|
|
|
|
|
<P>IMPORTANT NOTE: If you want the atom/indenter interaction energy to be
|
|
|
|
|
included in the total potential energy of the system (the quantity
|
2007-08-29 22:13:51 +08:00
|
|
|
being minimized), you must enable the <A HREF = "fix_modify.html">fix_modify</A>
|
2007-06-26 08:03:39 +08:00
|
|
|
<I>energy</I> option for this fix.
|
2006-09-22 00:22:34 +08:00
|
|
|
</P>
|
|
|
|
|
<P><B>Restrictions:</B> none
|
|
|
|
|
</P>
|
|
|
|
|
<P><B>Related commands:</B> none
|
|
|
|
|
</P>
|
|
|
|
|
<P><B>Default:</B>
|
|
|
|
|
</P>
|
|
|
|
|
<P>The option defaults are vel = 0,0,0 and units = lattice.
|
|
|
|
|
</P>
|
|
|
|
|
</HTML>
|
