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>min_modify command
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</H3>
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<P><B>Syntax:</B>
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</P>
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<PRE>min_modify keyword values ...
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</PRE>
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<UL><LI>one or more keyword/value pairs may be listed
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2009-02-26 08:18:18 +08:00
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<PRE>keyword = <I>dmax</I> or <I>line</I>
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2006-09-22 00:22:34 +08:00
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<I>dmax</I> value = max
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max = maximum distance for line search to move (distance units)
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2009-02-26 08:17:27 +08:00
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<I>line</I> value = <I>backtrack</I> or <I>quadratic</I>
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2009-02-26 08:18:18 +08:00
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backtrack,quadratic = style of linesearch to use
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</PRE>
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2006-09-22 00:22:34 +08:00
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</UL>
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<P><B>Examples:</B>
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</P>
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2008-04-15 05:37:10 +08:00
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<PRE>min_modify dmax 0.2
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2006-09-22 00:22:34 +08:00
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</PRE>
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<P><B>Description:</B>
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</P>
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2008-04-15 05:37:10 +08:00
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<P>This command sets parameters that affect the energy minimization
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2009-09-29 22:10:23 +08:00
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algorithms selected by the <A HREF = "min_style.html">min_style</A> command. The
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various settings may affect the convergence rate and overall number of
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force evaluations required by a minimization, so users can experiment
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with these parameters to tune their minimizations.
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2008-04-15 05:37:10 +08:00
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</P>
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2010-06-04 08:19:53 +08:00
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<P>The <I>cg</I> and <I>sd</I> minimization styles have an outer iteration and an
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inner iteration which is steps along a one-dimensional line search in
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a particular search direction. The <I>dmax</I> parameter is how far any
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atom can move in a single line search in any dimension (x, y, or z).
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2010-10-01 05:22:06 +08:00
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For the <I>quickmin</I> and <I>fire</I> minimization styles, the <I>dmax</I> setting
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is how far any atom can move in a single iteration (timestep). Thus a
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value of 0.1 in real <A HREF = "units.html">units</A> means no atom will move
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2010-06-04 08:19:53 +08:00
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further than 0.1 Angstroms in a single outer iteration. This prevents
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highly overlapped atoms from being moved long distances (e.g. through
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another atom) due to large forces.
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2009-02-26 08:17:27 +08:00
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</P>
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2009-09-29 22:10:23 +08:00
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<P>The choice of line search algorithm for the <I>cg</I> and <I>sd</I> minimization
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2010-06-04 08:19:53 +08:00
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styles can be selected via the <I>line</I> keyword. The default
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backtracking search is robust and should always find a local energy
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minimum. However, it will "converge" when it can no longer reduce the
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energy of the system. Individual atom forces may still be larger than
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desired at this point, because the energy change is measured as the
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difference of two large values (energy before and energy after) and
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that difference may be smaller than machine epsilon even if atoms
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could move in the gradient direction to reduce forces further.
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2009-02-26 08:17:27 +08:00
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</P>
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<P>By contast, the <I>quadratic</I> line search algorithm is often able to
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reduce forces closer to 0.0. It may also be more efficient than the
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backtracking algorithm by requiring fewer energy/force evaluations.
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However, it may not be as robust for some problems.
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2006-09-22 00:22:34 +08:00
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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 = "min_style.html">min_style</A>, <A HREF = "minimize.html">minimize</A>
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</P>
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<P><B>Default:</B>
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</P>
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2009-02-26 08:17:27 +08:00
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<P>The option defaults are dmax = 0.1 and line = backtrack.
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2006-09-22 00:22:34 +08:00
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</P>
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</HTML>
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