forked from lijiext/lammps
75 lines
2.6 KiB
HTML
75 lines
2.6 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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<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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keyword = <I>dmax</I> or <I>line</I>
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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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<I>line</I> value = <I>backtrack</I> or <I>quadratic</I>
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value = style of linesearch to use
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</UL>
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<P><B>Examples:</B>
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</P>
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<PRE>min_modify dmax 0.2
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</PRE>
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<P><B>Description:</B>
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</P>
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<P>This command sets parameters that affect the energy minimization
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algorithms. The various settings may affect the convergence rate and
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overall number of force evaluations required by a minimization, so
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users can experiment with these parameters to tune their
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minimizations.
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</P>
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<P>The minimization algorithms have an outer iteration (conjugate
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gradient or steepest descent) and an inner iteration which is steps
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along a one-dimensional line search in a particular search direction.
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The <I>dmax</I> parameter is how far any atom can move in a single line
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search in any dimension (x, y, or z). Thus a value of 0.1 in real
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<A HREF = "units.html">units</A> means no atom will move further than 0.1 Angstroms
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in a single outer iteration. This prevents highly overlapped atoms
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from being moved long distances (e.g. through another atom) due to
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large forces.
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</P>
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<P>The choice of line search algorithm can be selected via the <I>line</I>
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keyword. The default backtracking search is very robust and should
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always find a local energy minimum. However, it will "converge" when
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it can no longer reduce the energy of the system. Individual atom
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forces may still be larger than desired at this point, because the
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energy change is measured as the difference of two large values
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(energy before and energy after) and that difference may be smaller
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than machine epsilon even if atoms could move in the gradient
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direction to reduce forces further.
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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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</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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<P>The option defaults are dmax = 0.1 and line = backtrack.
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</P>
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</HTML>
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