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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>
<H3>min_modify command
</H3>
<P><B>Syntax:</B>
</P>
<PRE>min_modify keyword values ...
</PRE>
<UL><LI>one or more keyword/value pairs may be listed
<PRE>keyword = <I>dmax</I> or <I>line</I>
<I>dmax</I> value = max
max = maximum distance for line search to move (distance units)
<I>line</I> value = <I>backtrack</I> or <I>quadratic</I>
backtrack,quadratic = style of linesearch to use
</PRE>
</UL>
<P><B>Examples:</B>
</P>
<PRE>min_modify dmax 0.2
</PRE>
<P><B>Description:</B>
</P>
<P>This command sets parameters that affect the energy minimization
algorithms selected by the <A HREF = "min_style.html">min_style</A> command. The
various settings may affect the convergence rate and overall number of
force evaluations required by a minimization, so users can experiment
with these parameters to tune their minimizations.
</P>
<P>The <I>dmax</I> parameter is a bound on how far any atom can move in a
single dimension (x, y, or z) in a single iteration of the minimizer.
Thus a value of 0.1 in real <A HREF = "units.html">units</A> means no atom will move
further than 0.1 Angstroms in a single iteration. This prevents
highly overlapped atoms from being moved long distances (e.g. passing
through another atom) due to large forces. Note that for the <I>cg</I> and
<I>sd</I> style miminizers (see the <A HREF = "min_style.html">min_style</A> command),
<I>dmax</I> is a bound on the outer iteration or step along a search
direction, not a bound on the inner iteration of steps within a single
line search.
</P>
<P>The choice of line search algorithm for the <I>cg</I> and <I>sd</I> minimization
styles can be selected via the <I>line</I> keyword. Other minimizer styles
do not perform line searches, so they ignore this setting. The
default <I>backtrack</I> search is robust and should always find a local
energy minimum. However, it will "converge" when it can no longer
reduce the energy of the system. Individual atom forces may still be
larger than desired at this point, because the energy change is
measured as the difference of two large values (energy before and
energy after) and that difference may be smaller than machine epsilon
even if atoms could move in the gradient direction to reduce forces
further.
</P>
<P>By contast, the <I>quadratic</I> line search algorithm is often able to
reduce forces closer to 0.0. It may also be more efficient than the
backtracking algorithm by requiring fewer energy/force evaluations.
However, it may not be as robust for some problems.
</P>
<P><B>Restrictions:</B> none
</P>
<P><B>Related commands:</B>
</P>
<P><A HREF = "min_style.html">min_style</A>, <A HREF = "minimize.html">minimize</A>
</P>
<P><B>Default:</B>
</P>
<P>The option defaults are dmax = 0.1 and line = backtrack.
</P>
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